Our economy is continuously harmed by infestation of stored products brought about by stored grain pests which are responsible for worldwide loss of 10 - 40% annually. Tribolium castaneum (Herbst), Red flour beetle is a cosmopolitan and serious pest of cereal grains and their products. In order to manage the loss of stored grains and other agricultural products from insect infestation, many plant products have been evaluated for their toxic properties against different stored grain pests. In the present study, Bacillus thuringiensis isolates from collected samples were grown on T3 media. Bio-toxicity was checked individually and by combination of Black onion seed (Nigella sativa) and Bacillus thuringiensis, against Tribolium castaneum. The mortality data of Tribolium castaneum was analysed by applying probit analysis programme, determined that larvae are more susceptible and show significant results as compared to adults.