The objective of this study is to know effectivness of various antagonist microorganism (streptomyces sp., Bacillus, pseudomonas fluorescens and trichoderma sp.) for controlling leaf spot that caused by phaeotrichocornis crotalariae on seedling of acacia crassicarpa. This study was carried out in two phases, they are in vitro antagonistic test and in vivo antagonistic test in vitro antagonistic test was carried out according to multiple test method. a part of filterpaper 0,5 cm. in diameter was dipped on to suspension of each microorganism that would be tested and then dried to be put in to a petridish that contain P. crotalariae 0,5 cm. in diameter at PDA medium.