Cefotaxime sodium (CTX) was found to inhibit the activity of mushroom tyrosinase. The present study was conducted to investigate its inhibition of melanogenesis in B16F10 cells. CTX was found to inhibit melanin synthesis in B16F10 cells at a concentrations less than 200 μmol/L with no cytotoxicity. CTX reduced tyrosinase activity in a dose-dependent manner. CTX inhibited melanin formation from the results of the Masson-Fontana melanin staining and transmission electron microscope CTX influenced melanin production by influencing the expression of the proteins MITF, TRP-1, TRP-2 and TYR. Furthermore, CTX could down-regulate the intracellular cAMP/PKA/CREB contents, affecting the expression of MITF, and further down-regulate the expression of TRP-1, TRP-2 and TYR to inhibit melanin. Furthermore, CTX has been shown to inhibit body pigmentation in zebrafish. These results may provide a theoretical foundation for the new application of CTX in the field of medicine.