A simple and efficient method for determination of kasugamycin in chilli and soil was developed, and the fate of kasugamycin in chilli field ecosystem was also studied. Kasugamycin residues were extracted from sample, cleaned up by solid phase extraction and chromatographic column and then determined by ultra performance liquid chromatography with tandem mass spectrometry detection. The method got recoveries ranged from 77.82% to 83.35% with relative standard deviations of 2.20%-6.54%. As far as the accuracy and precision was concerned, the method met certain standard. The LODs of kasugamycin calculated as a sample concentration (S/N ratio of 3) was 2.50 μg kg(-1). The degradation of kasugamycin in chilli and soil was determined. The results showed that kasugamycin degradation in chilli plant and soil followed the first-order kinetics. The half-lives of kasugamycin in chilli and soil was 2.76-3.77 and 3.07-3.91 days, respectively. The final kasugamycin residues in chilli and soil were undetectable at levels of recommended and 1.5 times recommended dosage with an interval of 21 days.