Background: Undernutrition, anemia and low dietary diversity are the most common causes of morbidity and mortality among adolescent girls throughout the world, especially in South-East Asia and Africa. Even though adolescence is a window of opportunity to break the intergenerational cycle of undernutrition, adolescent girls are the neglected groups. rnObjective of this study is to assess nutritional status, low dietary diversity, anemia, and their associated factors among adolescent girls in Wolaita and Hadiya Zones, Southern Ethiopia. In addition to these this study has identified the barriers and facilitators of nutrition service utilization, and the effect of iron folic acid supplementation among adolescent girls in southern Ethiopia. rnMethods: This study was conducted in Wolaita zone and Hadiya zone. These Zones were selected purposely. The study has used a mixed study design (cross-sectional quantitative, qualitative, and randomized control). rnCommunity-based cross-sectional study was conducted from April 30/2019 to May 30/2019. A multistage sampling method was used to select a sample of 843 adolescent girls. A structured questionnaire was used to collect socio-demographic and dietary data through a face to face interview. Anthropometric measurement was collected from all adolescent girls and entered in WHO anthro plus software for Z-score analysis. Venous blood sample was collected from all selected adolescent girls. Hemoglobin level was measured in venous blood samples using a Hemocue photometer which was processed in the field (Hemocue R, Hb 301+ system). rnStructured 24-hour dietary recall (24HR) interview was conducted to capture detailed information about all foods and beverages consumed by the respondent in the past 24 hours, most commonly, from early morning to early morning of the previous day. In addition to this, a food frequency questionnaire was conducted to know usual frequency of consumption of food over the time period. rnData were entered in the computer using EPI-data 4.4.2 and exported to SPSS version 21.0 for further analysis. Variables which shown significant association (p-value â‰¤ 0.25) in the bivariate logistic analysis were included in the final multivariable logistic regression model. Odds ratios for logistic regression along with 95% confidence interval were estimated. P-value less than 0.05 were declared as level of statistical significance. rnFor qualitative study, health extension workers, school leader and gender focal person, health center expert and youth center leader from each village were involved in this study. For Focus group discussion: Eight adolescent girls in one group have participated from each village. For the selection of the participant, the purposive sampling method was applied to get the best information. Each audiotape interview was rnprofessionally transcribed word by word in wolaitegna and Hadiyagna (local language) and then translated to English. rnFor intervention study, community-based, individually randomized trial (RCT) was conducted at four villages of Wolaita and Hadiya zones from April to September 2019. During recruitment, adolescent girls age range in 10-19 years (226 in total) were randomly assigned to the intervention group (G1=113) and control group (G2=113). Weekly IFA supplementation was given to the intervention groups for three months, and nothing was given to control groups. For assessment of micronutrient status, 5ml venous blood sample was collected at baseline and at the end of the intervention. Primary outcomes were analyzed based on intention to treatment analysis principle. The prevalence of anemia was calculated based on the hemoglobin levels measured in venous blood samples using a Hemocue photometer which was processed in the field (Hb 301+ system). Specimens were transported on dry ice to the Ethiopian public health institute and analyzed for serum ferritin, serum folate and C-react protein by Immune turbid metric methods with a clinical chemistry analyzer (Cobas 6000 system; Roche Diagnostic GmbH) at the Ethiopian Public Health Institute. rnResults: Thinness (27.5%) and stunting (8.8%) were found to be public health problems in the study area. Age [AOR (95% CI) = 2.91 (2.03-4.173)], family size[AOR (95% CI) = 1.63(1.105-2.396)], monthly income [AOR (95% CI) = 2.54(1.66-3.87)], taking deworming tablet [AOR (95% CI) = 1.56(1.11-21)], fathers educational status [AOR (95% CI) = 2.45(1.02-5.86)], source of food for family [AOR (95% CI) = 5.14(2.1-12.8)], visit by health extension workers [AOR (95% CI) = 1.72(1.7-2.4)] and hand washing before eating and after using toilet [AOR (95% CI) = 2.25(1.079-4.675)] were significantly associated with thinness and stunting among adolescent girls in Wolaita and Hadiya zones, southern Ethiopia. rnThe mean (Â± SD) blood hemoglobin level of the study participants was 12.23Â±1.16 g/dL and 37% of the study participants were moderately anemic (Hg 7-12gm/dl) and 0.2% of the study participants were severely anemic (Hg