The study was carried out to quantify the purity of different marketed brands of three insecticide namely diazinon, acephate and cypermethrin using suitable protocols GC-FID and GC-ECD. Nineteen marketed brands of these insecticides collected from retailers of Jessore, Gazipur and Rangpur region were analyzed and estimated their purity in two seasons of 2006-2007 and 2007-2008. Among six marketed brands of diazinon, only one brand (RSN) had 96.71-100% purity in both the seasons in all locations which considered to be standard product, but four brands (DZN, SBN, HZN, DNN) in other regions, contained <95% pure which were substandard product. The remaining 2 brands (DNN, AZN) contained 33.71-51.94% purity in 2006-07 and the other two brands (SBN, DZN) had very small amount of active ingredient (0.16-0.84% purity) in 2007-08 and all these were impure in quality. All five tested brands of acephate had 57.14-88.59% purity in 2006-07 which were substandard but in 2007-08, three brands (SNT, BNS, ATF) showed >90% purity and the remaining 2 had <80% purity which were less AI than required. Of eight tested brands of cypermethrin, three brands were almost to have >95% pure in 2006-07 in all locations. The other two brands (CPR, AMT) contained >90% purity. In 2007-08, two brands of cypermethrin (RCD, SCR) contained >95% pure, another two brand (CRN, RLT) had 88.77-91.15% purity. The brands UTD was standard in purity in 2006-07 but this brand was below standard in quality in 2007-08 in all locations. Most of the tested brands of cypermethrin were found standard and sub standard level of purity in comparison to diazinon and acephate.