The reduction of m-Dinitrobenzene (m-DNB) to m-nitroaniline (m-NA) with selenium and hydrazine hydrate was studied under mild conditions. The effects of ratio of solvents, hydrazine hydrate amount, selenium amount and NaOH amount on the reduction of m-DNB to m-NA were investigated. The results show that selenium has high catalytic activity and selectivity for the reduction under mild conditions. Under the optimized conditions of V(ethanol)/V(water) = 10∶1, 2 mmol of m-DNB, 3.1 mmol of hydrazine hydrate, 0.04 g of NaOH, 0.02 g of selenium, 75 ℃ and 2 h, the m-DNB conversion and the m-NA selectivity can reach 100 % and 98.7 %, respectively.