Microbial degradation of pendimethalin and the effects of culture conditions in vitro are studied. Twenty-nine strains are isolated by enrichment from soil and sludge. 3 strains can degrade more than 80% of pendimethalin of 100 mg x L(-l) in 3 days in culture fluid. 2 bacteria are considered as efficiently degrading strains identified as Pseudomonas, Mirococcus luteus. The efficiency of degradation is affected by culture conditions such as pH, temperature and the concentration of sucrose and pendimethanlin. The optimal conditions are proposed.