Abstract : The liquid waste of the tanning industry contains chromium metal of a toxic nature. The heavy metal chromium has high solubility and toxicity and is toxic to living things with a concentration of more than 0.05 ppm. For this reason, it is necessary to conduct a toxicity test to determine the level of danger from wastewater if it is discharged into the environment. The purpose of this study was to determine the value of LC concentration of 50 96 hours from tanning liquid waste to tilapia mortality (Oreochromis niloticus). The method used in this study is an experimental method. The data used is in the form of primary data and secondary data. The measured wastewater parameters are temperature, pH, BOD, COD, TSS, Cr, oil and fat, ammonia, sulfide, and nitrogen. Data analysis using probit analysis. The results of this study show that LC 50 96 hours is 261,3 ppm, so tanning wastewater needs to be treated first before being discharged into the environment.