The objective of this study was to evaluate the antagonistic effects of lipid on surfactant inhibition in anaerobic digestion. The preliminary results indicated that the typical surfactant of sodium dodecyl sulfate (SDS) exerted a strong inhibitory effect on anaerobic digestion with IC50 of 80 mg/L. Interestingly, the presence of lipid (soybean oil) effectively alleviated the SDS inhibition with an antagonistic enhancement. Gompertz model fitting results indicated that in the presence of 0.5 g/L, 1.0 g/L and 1.5 g/L of soybean oil (SO), the lag phases (lambda) were shorten to 78 +/- 8%, 25 +/- 5% and 15 +/- 0%, respectively, and the maximum CH4 production rates (R-max) were increased to 153 +/- 7%, 161 +/- 9% and 199 +/- 0%, respectively. On the other hand, the presence of surfactant enhanced the degradation of lipid. In addition, the supplementing of lipid in late stage was found to be effective to recover the activity of surfactant-inhibited anaerobic digestion. Microbial analysis showed that SO enhanced the growth of syntrophic bacteria of Proteobacteria and acetoclastic methanogens of Methanosaeta. The antagonistic mechanism might be ascribed to the interaction between surfactant and lipid which obstructed the adsorption of surfactant onto cells, and thereby relieving the surfactant inhibition.