The residue of organochlorine pesticides (OCPs) has been a major pollution problem in our environment. Dichlorodiphenyltrichloroethane (DDT) is one of the most common persistent OCPs that continue to pose a serious risk to human health and the environment. Some treatment methods have been developed to reduce and minimize the adverse impacts of the use of DDT, including biodegradation with brown-rot fungi (BRF). However, DDT degradation using BRF has still low degradation rate and needs a long incubation time. Therefore, the ability of BRF need to be enhanced to degrade DDT. Interaction and effect of bacteria addition on biodegradation of DDT by brown-rot fungus Daedalea dickinsii were investigated. The interaction assay between D. dickinsii with bacteria addition showed that the addition of bacterium Pseudomonas aeruginosa did not provide resistance to the growth of D. dickinsii. Meanwhile, bacterium Bacillus subtilis addition has an inhibitory effect on the growth of D. dickinsii. The addition of 10 ml (1 ml = 1.05 x 10(9) CFU/ml bacteria cell) of P. aeruginosa and B. subtilis was able to improve DDT biodegradation by D. dickinsii from 53.61% to 96.70% and 67.60%, respectively. The highest biodegradation capability of DDT was obtained through addition of 10 ml of P. aeruginosa into the D. dickinsii culture in which the mixed cultures produce final metabolites of 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane (DDD) and 1-chloro-2,2-bis(4-chlorophenyl)ethylene (DDMU). This study indicated that the addition of P. aeruginosa can be used for optimization of DDT biodegradation by D. dickinsii.