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Defatted microalgal biomass (DAB) of a local Scenedesmus dimorphus strain was characterised as animal feed in an experimental Wistar rat model. The DAB contained 21.5 % protein, 28 % dietary fibre and 21 % ash on dry basis. The DAB was rich in calcium (1208 mg 100 g biomass) followed by magnesium (400.6 mg 100 g) among the tested mineral elements. The essential amino acids (EAA) constituted 48 % ( w/ w) of proteins, and the EAA index was similar to casein and soybean. The protein was limiting in sulphur-containing amino acids cysteine and methionine. The algal biomass showed 5-6-fold higher water absorption capacity (3.44 ± 0.06 g g biomass) compared with basal diet (0.67 ± 0.06 g g biomass). The DAB was found to be safe in both short-term (14 days), single-dose feeding (20 % ( w/ w) feed) and long-term (90 days) repeated-dose feeding (at 5 and 10 % ( w/ w) feed). In the short-term feeding trial, faecal output and water intake increased by 2-fold during the initial 4 days, mainly attributed to higher ash and fibre content of biomass. The long-term repeated-dose feeding of DAB did not induce any physiological changes in rats such as feed intake, haematology profile, serum biochemical parameters, histopathology and relative organ weight. The feed conversion ratio and quotient of protein efficiency ratio in DAB-fed groups were similar to control. However, animals required a longer adaptation period to DAB-mixed feed, as indicated by slower body weight gain and feed intake. The study suggests that DAB can be used as animal feed up to 10 % ( w/ w) replacement levels. [ABSTRACT FROM AUTHOR]