In this research, a method based on base catalyzed decomposition (BCD) was developed using bases and glycerol for dechlorinating of transformer oils with low levels of polychlorinated biphenyls (PCBs) and contaminated soils. Also quality of refined oil and mechanism of dechlorination in this method was studied by gas chromatography and silver nitrate titration method. By using sodium hydroxide, PCBs Dechlorination efficiency after 4 hours at 250?C with and without iron were 97.4 and 79.5 percent, respectively. While PCBs removal efficiency with and without iron were 99.8 and 99.7 percent, respectively. Use of iron, besides increasing conversion rates, changed the mechanism of the reaction from nucleophilic substitution to combination of hydrodechlorination and nucleophilic substitution. Because of inefficiency of dechlorination efficiency, the Recovery parameter was defined as the ratio of chlorine atoms detected by the chromatograph and the chlorine ions contained in the residual divided by all the initial chlorine atoms. Recovery after 4 hours at 250?C with and without iron were 80 and 97/4 percent, respectively. Color, breakdown voltage and dielectric loss factor of Oils refined at 250 ?C did not meet the necessary standards to be reused in the transformer but those refined at 200 ?C, satisfied the standards with acceptable conversion rates. By using sodium hydroxide, PCBs removal efficiency after 4 hours at 250?C in artificial soil were 97 percent and 10 percent of total PCBs remained in glycerol. While these values for the lime were 97 and 76 percent, respectively. PCBs were blocked using quicklime with a solidification and sedimentation mechanism on the soil, while were dechlorinated using sodium hydroxide .Clay soils were cleaned with less efficiency due to the sticky structure than sandy loamy soils. In natural soil, using lime after 7 days, 65% of PCBs was decreased, of which 26% was due to solidification in the structure of calcium silicate hydrate. By using sodium hydroxide, PCBs removal efficiency after 4 hours at 250?C in artificial soil were 84 percent and 12 percent of total PCBs remained in glycerol. Keywords: PCBs, Transformer Oils, Soil, Glyserol, Sodium Hydroxide, Iron