Phytotoxic effects of soil incorporation with Goniothalamus andersonii bark powder against Cucumis sativus (cucumber), Trifolium repens (white clover), Lactuca sativa (lettuce), and Lolium perenne (perennial ryegrass) were evaluated under the greenhouse condition for possible utilization as weed suppression. The growth of tested plants was reduced significantly after 14 days of incorporation where the degree of inhibition was dose dependent. A monocotyledonous plant, L. perenne was greatly inhibited by 94.8% when exposed to the bark powder concentration of 2% (w/w). After 21 days of incorporation, the length and fresh weight of both root and shoot part of tested plants were decreased significantly. These results indicate that G. andersonii bark possess inhibitory activity against various tested plants, suggesting that the bark powder is very beneficial as natural herbicide in weed control management.