Abstract: The determination method of determining cyanide in wastewater by isonicotinic acid barbituric acid was introduced in this paper. The optimum condition of spectroscopic measurement was determined and the measuring wavelength was 598 nm. The standard recovery rate to wastewater is between 98 3% and 102 5%, This method was comparable to the pyridine barbituric acid and isonicotinic acid pyrrazolone method.