BACKGROUND: In this study, batch experiments were conducted using diesel-contaminated soil collected from a former gas station to evaluate the efficiency of diesel removal by in situ chemical oxidation (ISCO) and the effects of different oxidants on the indigenous microbial community. RESULTS: Diesel removal efficiencies by persulfate, permanganate, and hydrogen peroxide under different concentrations (1, 3, 5, and 10%) ranged from 48 to 93% during a 120-day reaction. The performance of diesel removal in the oxidant-alone systems was persulfate>permanganate>hydrogen peroxide. Oxidant persistence was positively correlated with diesel removal performance. Higher diesel removal efficiencies were observed in the chemical oxidation systems with the presence of microbes. The adverse effects of the oxidants on intrinsic microbes followed the sequence persulfate>permanganate approximate to hydrogen peroxide. The addition of hydrogen peroxide and permanganate caused increased microbial diversity while more serious destruction to the microbial community was observed in the persulfate solution due to low pH (<3.5). CONCLUSION: The results suggest 1 to 3% of oxidant addition was more suitable for the application of ISCO coupled with intrinsic bioremediation. The addition of 5% oxidants could also be considered. However, pH should be controlled when persulfate is applied. (C) 2015 Society of Chemical Industry