Indoor air pollution due to combustion of biomass fuel is a common practice in ruralrnhouseholds of developing countries. Young children living in households exposed to solidrnfuel have greater risk of developing acute respiratory infections. The main objective of thisrnstudy is to evaluate the effect of indoor air pollution from household biomass fuel use andrnacute respiratory infection in younger children of Anilemo woreda, southern Ethiopia. Thisrnstudy was designed as a cross sectional exposure assessment that was carried out in 150rnhouseholds that have children of age less than five years spread across selected three ruralrnkebeles. The survey instrument was specific structured questionnaire that was adapted fromrnWHO guidelines for survey of household fuel use and acute respiratory infections. Thernsurvey defined Children who suffered from cough accompanied by short, rapid breathingrnduring the two weeks preceding the survey defined as having suffered from acute respiratoryrninfections (ARI). Concentration of total suspended particles(TSP) and carbonmonooxidern(CO) were measured in small subset of (10%) sampled households during the cooking andrnnon cooking hours using SKC 224-PCTX4 model air sampling pump and EL-USB- COrnlogger, respectively. Data was analyzed using SPSS version 20. Logistic regression analysisrnwas used to determine the association of household fuel using characteristics to ARI andrndescriptive statistics such as frequency distributions and measure of central tendencies werernused to describe concentrations of total suspended particulates and carbon monoxide. Thernresult of the study revealed that biomass fuel is a dominant fuel type at household level andrnestimated the overall prevalence of acute respiratory infections (ARI) among youngerrnchildren is 26.7% in two weeks period prior to the survey. Ventilation status of rooms, childrnholding on back during cooking, Patterns of time-activity, which place children near sourcesrnof pollution such as cooking stoves and number of younger children living in a house werernconsistently associated factors to the prevalence of ARI. The mean cooking and non cookingrnhour concentrations of total suspended particles in (Î¼g/m3) and carbon monoxide in (ppm)rnwere 6794.96 and 10.45; 4854.81 and 4.42, respectively. The highest average concentrationsrnof TSP and CO were observed in households using mixed fuels during cooking timesrn(13312.50 Î¼g/m3 and 52.10ppm). The total mean cooking hour concentration for TSP is 1.4rntimes higher than the total mean non cooking hour concentration of TSP. The total meanrncooking one hour concentration for CO is 1.6 times higher than the total mean non cookingrnone hour concentration. The 10.45 ppm CO mean concentration measured in this studyrnwhich is a marginal level in reference to potential or foreseeable problems in somernsituations.rnThe practice of using biomass fuel and traditional unvented stoves at rural household levelsrnaggravates the exposure to indoor air pollutants. Therefore it is crucial to further investigaternand include the indoor air pollution issues as an integral part of addressing the healthrnproblems of younger children.rnKey words: Household biomass fuel, ARI, Indoor air Pollution, Anilemo