Background: Oseltamivir phosphate (OP) is preferred treatment for influenza with activity against influenza A and B. It is commonly recommended for the treatment and chemoprophylaxis in pregnancy and lactation. Serious neuropsychiatric adverse reactions were observed in patient treated with OP. Objective: This study aims to evaluate the effects of OP on prenatal and post-natal development of the albino rat cerebellar cortex. Material and methods: This study was carried out on 40 pregnant albino rats and 120 of their offspring of both sex, 3 from each mother. The pregnant rats were divided equally into 2 main groups A and B. Group A (control): it was subdivided equally into 2 subgroups A1 and A2. Group B (OP treated): it was subdivided equally into 2 subgroups B1 and B2. In group A, each rat mother was given 0.9 ml distilled water twice daily by oral gavage for successive 5 days. In group B, each rat mother was given 0.9 ml distilled water containing 1.35 mg OP twice daily by oral gavage for successive 5 days. Dosing started from the 15^th to 19 ^th of pregnancy in subgroups A1 and B1 while it started from the 1^st to 5^th day after delivery in subgroups A2 and B2. Cerebelli were collected, on the 1^st day of birth in subgroups A1 and B1, on the 7 ^th day of birth in subgroups A2 and B2, and on the 14 ^th day of birth in subgroups A1, A2, B1 and B2. The cerebelli of all subgroups were subjected to light microscopic study and the cerebelli of 14 days old offspring were subjected also, to transmission electron microscopic and morphometric studies and statistical analysis. Results:  OP induced delayed development and neurotoxic effects on the cerebellar cortex of albino rat offspring whose mother dosed OP during pregnancy or during lactation. Conclusion: Oseltamivir phosphate induced pre and post-natal delayed development and neurotoxic insults on the cerebellar cortex of albino rat.