The objective of this study is concerned about the effects of ultrasound, KPEG/oil weight ratio and polyethylene glycol (PEG) molecular weight in the treatment of PCBs present in transformer oil using chemical dechlorination (KOH/PEG). The dechlorination performance was assessed in terms of the destruction and removal efficiency (DRE) of PCBs. DRE value was expressed as percentage. An Agilent 7890A Gas Chromatograph (GC) fitted with a flame ionization detector (FID) and a capillary column (HP-5) was used for the determination of PCBs. The best results (average DRE of 88.55 %) were obtained under the following conditions KPEG/oil ratio of 30 and PEG 600. PCBs dehalogenation in Sovtol-10 involves all congeners with high efficiency. In particular, congeners of high molecular mass disappear from the chromatogram in all runs. The removal of PCBs is strongly affected by KPEG/oil ratio, PEG and KPEG/oil ratio-PEG interaction, in this order