Abstract: Thrips tabaci Lind. is a major pest of greenhouse cucumber, Cucumis sativus L. in Khuzestan province, Iran. Greenhouse evaluations were conducted to determine effectiveness of Orius laevigatis Fieber inundation at different release rate to control of T. tabaci in greenhouse cucumber. Population densities of T. tabaci and O. laevigatus were weekly monitored and cucumber fruits were weekly harvested and graded in the different experimental treatments. Twice releases of O. laevigatus with two weeks interval at inundative rate of one and three predatory bugs per plant could not significantly suppress the thrips population and decrease percentage of unmarketable fruit yield (Pum) during whole of trial period. Periodical inundation of three predatory bugs per plant every two weeks could effectively control T. tabaci population and significantly reduce Pum in comparison to control treatment. Results showed that O. laevigatus could not establish on greenhouse cucumber in south of Iran. As a conclusion, this predatory bug can not provide a sustainable control of T. tabaci on greenhouse cucumber in south of Iran. Use of other Orius species should be evaluated to biological control of T. tabaci on greenhouse cucumber.