The cyanobacterium Arlhrospira (Spirulina) is known for its high protein content and havingrnvarious bioactive phytochemicals with potential health benefits. It is, therefore, producedrnworldwide either artificially or directly from natural lakes to be used as a dietary and/or proteinrnsupplement. Spirulina grows abundantly almost as a uni -algal population in an Ethiopian sodarnlake, Lake Chitu throughout the year. The objective of this study was to evaluate the nutrientrnprofile and safety of Lake Chitu's Spirulina for possible applications in human nutrition. A onernyear study (March 2012-January 2013) was undertaken where sampling was done at two monthsrninterval. Variations were observed in the nutrient profile of the biomass on seasonal basis and inrngeneral wet season samples had relatively higher protein (47.9-55.7%) and low carbohydratesrncontents (30.9-36.4%) compared to dry season samples. Higher amino acids content wasrnrecorded for a wet season sample (86.4g/100g protein) compared to a dry season samplern(62. l g/I00g protein). Variations were also observed in the fatty acid composition of LakernChitu 's Spirulina as relatively higher proportion of unsaturated fatty acids were recorded for arnsample harvested in wet season (61.8%) compared to a dry season sample (58.2%). Similarly,rnhigher contents of phylonutrients (pigments) (mg g.I): chlorophyll a (8.2-10.3),rnphycobiliproteins (104.1-120.7), total carotenoids (3.17-4.31) and ~-carotene (1.24-1.61) werernrecorded for wet season samples. The mineral content of the biomass also varied according tornseason. While Na and K were found to be higher in the dry season sample, other major (Ca, P,rnMg) and trace (Mn, Fe, Cu, Zn and Se) minerals were found in higher concentrations in the wetrnseason sample.rnThe safety of Lake Chitu's Spirulina was evaluated in terms of its microbial profile, heavyrnmetals, pheophorbides, microcystin and nucleic acids content. Aerobic mesophilic count of thernbiomass ranged from 0.4 xl03 to 130 xl03 CFU/g for wet season and from 0.37 xlO3 to 15 xlO3rnCFU/g for dry season samples. Counts of total coliforms, fecal coliforms, Ecoli, S. aureus,rnyeasts and molds were < 102CFU/g for both wet and dry season samples. Heavy metal contentsrnof the biomass (mg kg-I) were: Pb (0.18), Cd (0.03), Hg (0.04) and As (18 .8). Pheophorbidesrncontent of the biomass were 16.2mg/100g and 22.3mg/J OOg for wet and dry season samplesrespectively. The nucleic acids content of the samples were 0.18 and 0.13% for wet and dryrnseason samples respectively. Microcystins were not detected in both wet and dry season samplesrnand short term feeding offreeze dried biomass (10 g/kg body weight) to mice didn't result anyrnsigns of toxicity or mortality.rnPhycobiliprotein-rich crude extract (PBE) was prepared from Spirulina and was evaluated for itsrnchemical composition, amino acid profile, in vitro protein digestibility and functional propertiesrnfor possible food applications. Phycobiliprotein-rich crude extract had higher contents of proteinsrn(60.1 vs 45.2%) and amino acids (45.6 vs 39.0g/100gsample) than the crude Spirulina powder.rnSimi larly, in vitro protein digestibility value of PBE was higher (86%) than the crude Spirulinarnpowder (59%) in a single enzyme assay. The extract had 50.5% protein solubility at pH 7 andrn62.2% solubility at pH 12 although at this pH discoloration of the pigment was noted . PBErnshowed good emulsifying activity at neutral and basic pH regions and at higher proteinrnconcentrations the extract showed comparable emulsifYing activity with bovine serum albumin.rnSimilarly, the foaming capacity and stability of PBE were high and comparable with therncommonly used foaming agent, egg albumin.rnIn conclusion, the nutrient profile of Lake Chitu's Spil'ulina is comparable with that reported forrncommercial Spirulina. Except arsenic which was found in higher concentrations, the biomass isrnsafe in terms of other safety evaluation parameters and thus can potentially be used in humanrnnutrition. In addition to using the whole biomass as a food supplement, high value products suchrnas phycobiliproteins can be extracted from the crude biomass which can serve as a component inrnfunctional foods.rnKey words: Arthrospira, biomass quality, functional property, Lake Chitu, safety, season,rnphycobiliproteins, Spirulina