Sasa (Sasa cernua Makino) is a very serious weed pest. Its allelopathy was studied using lettuce, wheat, timothy, and green amaranth as testing species. Cultured in the rhizosphere soil ofSasa cernua, the seedlings were inhibited by 42-80% compared with the controls cultured in normal soil and vermiculite. The phenolic fraction extracted with 1 M NaOH from the rhizosphere soil ofS. cernua caused significant inhibitions on the seed germination and seedling growth of lettuce, timothy, green amaranth, and barnyard grass.p-Coumaric, ferulic, vanillic, andp-hydroxybenzoic acids andp-hydroxybenzaldehyde were identified as the main allelochemicals in sasa soil by HPLC and [(1)H]NMR. Their contents in the rhizosphere soil were 5640, 1060, 860, 810 and 630 μg/100 g soil. The neutral fraction inhibited the seed germination and seedling growth of lettuce in the TLC direct bioassay. Volatile compounds released from sasa leaves also inhibited the growth of lettuce, wheat, timothy, and green amaranth grown under light, and the growth of etiolated seedlings of barley and wheat. These results confirm thatS. cernua produces typical allelopathy through its rhizosphere soil and air space.