This research was carried out to find the dyeabilities and mordants effects of cow leather dyed with Lac powder. They were examined by changing dye concentration, dyeing temperature, bath ratio, dyeing time, and dyeing repetition. And K/S values and surface color changes were evaluated by various mordanting conditions. The optimum dyeing conditions of the cow leather dyed with Lac powder were 30%, 40℃, 30:1, 30minutes, and 4 repetitions. The K/S values were higher in post mordant than pre mordanting condition. The surface colors of dyed cow leathers were R and RP. The dye fastnesses increased in post Cu and Fe mordanting, as decreased in gallnut and chestnut`s skin conditions.