Senna didymobotryaFresenis one of the 18 Senna species growing in Ethiopia. The plant is known for its value in traditional medicine. The present study was carried out on the phytochemical analysis and antimicrobial activity of seed extracts ofSenna didymobotrya. Seed was extracted with n-hexane, chloroform: methanol (1:4) and methanol through soxhlet apparatus to get crude extracts. The crude extracts were subjected to phytochemical test which shows the presence of tannins, saponins, terpenoids, phenols, alkaloids and steroidal rings. Chloroform: methanol (1:4) crude extract was subjected to column chromatography to get fraction 3. All extracts and fraction 3 were tested for antibacterial and antifungal activity. The maximum antibacterial activity was shown by the methanol crude extract to against Escherichia coli with an inhibition zone of 17.16mm. The maximum antifungal activity was shown by chloroform: methanol(1:4) crude extract against Aspergillus niger with an inhibition zone of 22.3 mm. The fraction 3 exhibited medium activity towards Staphylococcus aureus, Streptococcus pyrogenes and Escherichia coli (E. coli). These results have shown that Senna didymobotryaseed extracts had significant activity against all the organisms tested.