The study was undertaken to calculate the uncertainty of results, related to the analysis of 28 pesticides present in green chilli. Gas Chromatography Electron Capture Detector was used for the analysis of above pesticides present in green chilli. Bottom-up approach was taken for calculation of uncertainty sources arise from weighing, purity of standards, repeatability, calibration and recovery study. To calculate the total uncertainty, relative uncertainty due to purity of standard (U1), due to weighing (U2) and precision (U3) are considered. The combined uncertainty (U) was calculated by equation: U = [(U1)2+(U2)2+(U3)2]1/2. Expanded uncertainty (2U) was twice of combined uncertainty (U) at 95% confidence level. Combined uncertainty values lies between 0.0007-0.0035. Percent uncertainty of almost all the pesticides taken for study was found below ≤10% except beta HCH percent uncertainty value is 11% lies in 11-15% range and lambdacyhalothrin value is 16% lies in 15-20% range.