The leafminer, Liriomyza sativae is the major leaf pest of tomato and cucumber fields. It reduces economically yield in outbreak conditions. The farmers use insecticides more times per season against the pest. It is necessary to register new insecticides with different mode of action and low-risks. In this investigation, thiocyclam as a new and biorational insecticide was studied against leafminer. This research carried out in West Azarbaijan province in 2011. Results showed that all treatments had acceptable efficacy in tested location. The mean efficacy of abamectin (0.15 ml/L), cyromazine (0.3 g/L) and thiocyclam (0.75 and 0.5 g/L) were 77%, 70.5%, 82.25% and 76.25%, respectively. Due to same efficacy of both thiocyclam treatments, it can be applied with low concentration (0.5 g/L). The most decreasing of large and small mines were observed in thiocyclam 0.75 treatment (34.97% and 38% respectively). But the lowest were noticed in cyromazine 0.3 treatment (15.59% and 13% respectively). Results indicated that thiocyclam had larvicide activity and adult toxicity.