Purpose: The use of sodium hypochlorite (NaOCl) can decrease the bond strength of 4-META/MMA-TBB resin cement to root dentin. The aim of this in vitro study was to evaluate the effect of sodium toluene sulfinic acid (SA) as a pretreatment to increase bond strength to NaOCl-treated dentin. Materials and Methods: The root canal dentin of bovine teeth was treated with 6 methods: group 10-3 (10% citric acid/3% ferric chloride; control); group SA; group NC (sodium hypochlorite/10-3 solution); group NS-10-3 (NaOCl + sulfinic acid + 10-3 solution); group HSA-10-3 (NaOCl +H2O2 +NaOCl + sulfinic acid + 10-3 solution); group HO-10-3 (NaOCl + H2O2 + NaOCl +10-3 solution). The roots were then filled with Super-Bond C&B (SB) or Super-Bond sealer (SBS). Samples were stored in distilled water for 24 h at 37°C and then cross sectioned into five slabs (0.8 mm thick) that were subjected to "trimming" microtensile bond strength testing. All treated dentin surfaces and resin/dentin bond interfaces were analyzed under SEM. Results: Compared with the control, NaOCl treatment significantly decreased the resin/dentin bond strengths. However, SA treatment following NaOCl irrigation resulted in no significant differences of bond strength values. Conclusion: Sulfinic acid was effective in restoring 4-META/MMA-TBB resin cement bond strength after NaOCl irrigation. Keywords: dentin bond strength, resin cement, sodium hypochlorite, sodium toluene sulfinic acid