Abstract: The new method for the determination of active ingredient in chlorothalonil by HPLC on 250×4.0mm Lichosorb Si60- 5μchromatographic column with 254nm UV-detector was established.The mobil phase was n-heptane _ methylene chloride (80:20v/v) and flow rate was set at 1.2ml/min,The method was simple, rapid,accurate and practical. The linear correlation were 0.03mg/ml-1.2mg/ml,the recovery were 99.01%-100.72%,the coefficients of variation were 0.277%.