Slop wax waste by-product obtained through the lube oil manufacture was subjected to biotreatment using five isolated Bacillus species at 30 degrees C and various incubation periods, 7, 14 and 21 days. The results obtained from HPLC for the 15 samples showed that the aromatic contents decreased, especially, for that treated with Bacillus sp. MAM-27 which degrade PAHs faster at 1% (w/v) concentration of slop wax waste by-product and exhibited high biodegradation ability within 1 week. Bacillus sp. MAM-27 degraded 99.9% of PAHs, while Bacillus sp. MAM-24 degrades 99.8% of PAHs within 2 weeks and then the degradation ability is slightly increased afterwards. The gas chromatographic analysis of the samples before and after treatment with Bacillus spp. showed that, the aromatics, naphthenes and iso-alkanes were more degradable than saturated n-paraffins. Treatment by Bacillus sp. MAM-27 and Bacillus sp. MAM-24 can be an effective method for biodegradation of slop wax waste by-product leading to paraffin waxes match with plastic paraffin wax according to USSR 1121284 specifications. (C) 2011 Elsevier B.V. All rights reserved.