Monster 40 EC was applied to eggplant plants. Its fate in fruits was studied. There were twoapplications in our treatments as following one application of 8g a.i. acephate/8L water and one application of 32g a.i. acephate/8L water. Samples of eggplant were random collected from treated plants after a time elapse of 0 (three hours), 2, 4, 6,…, and 60 days after insecticide treatments. The quantitative determination of acephate and methamidophos were done by GC-MS. Investigating the relationship between acephate and methamidophos demonstrated that 6.3 -13.5% of acephate was degraded into methamidophos in eggplant fruits. The calculated half-life of acephate was 4.3 days. The methamidophos was found to be more persistence than acephate with 11.4 days. The evolution of the acephate and methamidophos concentration behaviour in eggplant led to the behaviour empirical equations: Y = 1.926t0.55e-0.21t for acephate (one application of 8g a.i. acephate/8L water), Y = 4.029t0.676e-0.228t for acephate (one application of 32g a.i. acephate/8L water), Y = -0.0007t2+ 0.0197t+ 0.016e-0.134t for methamidophos (one application of 8g a.i. acephate/8L water) and Y = -0.0008t2+0.027t+0.036e-0.134tfor methamidophos (one application of 32g a.i. acephate/8L water).