Abstract: Four bisbenzylisoquinoline alkaloids (Ⅰ～Ⅳ)have been isolated from the roots of Cocculus trilobus DC. (Menispermaceae) growing wild in the mountainous areas of Zhejiang province. Their structures were established as isotrilobine (Ⅰ), trilobine (Ⅱ), isotrilobine- N- 2-oxide (Ⅲ)and nortrilobine (Ⅳ)on the basis of spectral analysis (UV, IR, HNMR, MS), physico- chemical constants and properties of the derivatives. Ⅲ is a new alkaloid and Ⅳ was found from this plant for the first time.