Salvianolic acid B (Sal B) is one of the major water-soluble compounds isolated from Radix Salviae Miltiorrhizae (Danshen in Chinese) that has been reported to be beneficial to treatment of diabetic complications. However, the mechanisms involved in these effects are not discussed in relation to mesangial proliferation via modulation of NF-κB. To explain this, human mesangial cells were pretreated with or without Sal B (0.1, 1, 10 μM) for 24 h and stimulated with high glucose (30 mM). Then the effects of Sal B on mesangial cells proliferation, extracellular matrix production and the possible mechanisms were evaluated by methylthiazoletetrazolium assay, flow cytometry assay, enzyme-linked immunosorbent assay, gelatin zymography assay and western blot assay. These results indicated that Sal B could inhibit high glucose-induced mesangial cells proliferation and extracellular matrix production in a dose-dependent manner, partially through modulating the cell-cycle progress and MMP-2 and MMP-9 activities via suppressing NF-κB activation, suggesting that Sal B may be a promising agent for treating diabetic nephropathy.