The field experiment was conducted at Spices Research Centre, Shibganj, Bogra, Bangladesh during Rabi season of 2016-17 to evaluate the efficacy of different bio-rational insecticides for the management of thrips of onion. Six treatments were replicated three times in randomized complete block design. The treatments were T1= Spraying of Beauveria bassiana @ 5g/litre of water; T2= Spraying of Metarhizium anisopliae @ 4g/litre of water; T3= Spraying of Spinosad (Success 2.5 SC) @ 1.2ml/litre of water; T4= Farmers practice- Three spraying of Dimethoate (Tafgor 40EC) @ 1ml/litre of water; T5= Control (Water +Sticker i.e Trix @ 5ml/litre of water) and T6= Absolute control. All the insecticides were significantly better than absolute control in reducing thrips population after every spray. It was evident from the study that significantly lowest (4.30 thrips/plant) thrips populations were recorded from bio-pesticide Spinosad treated plot followed by farmers practice (7.95 thrips/plant) and Beauveria bassiana (8.46 thrips/plant) at 4th day after 3rd spray. Maximum marginal benefit-cost ratio was also obtained from Spinosad treated plot (33.09) followed by farmers practice (30.62) and Beauveria bassiana (15.96). This study showed that bio-pesticide Spinosad (Success 2.5 SC) @ 1.2 ml/litre of water three times at an interval of 10 days from the first appearance of thrips infestation may be recommended for the management of thrips of onion.