Medicinal plants are abundant in Myanmar. In the present research, the root of Stemona curtisii Hook. F. was chosen for investigation of some phytochemical constituents and bioactivity studies. Acute toxicity of 95 % ethanol extract from roots sample was investigated by methods of OECD guidelines for the testing of Chemical 425. Screening of root extract was done with the dosage of 2000 mg/kg, 300 mg/kg and 50 mg/kg body weight in albino mice. Antimicrobial activity of pet- ether, methanol, ethyl acetate, 95 % ethanol and watery extracts from roots of S. curtisii was investigated against six species of microorganisms such as Bacillus pumilus, Bacillus subtilis, Candida albicans, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus species by agar well diffusion method. Among them, ethyl acetate and methanol extracts of S. curtisii exhibited inhibition zone diameter in the ranges of (12 15 mm) and (11 20 mm) against all tested microorganisms. According to the results, it can be inferred that root of S. cutrisii may be used as remedy for the treatment of diseases related to the microorganisms tested.