The present study was conducted to test the toxicity of neem oil with Prosopis juliflora as abotanical synergist. Different concentrations of botanical synergist were used with neem oil and incubated for 1hrs at 150rpm and at 40oC. After incubation, toxicity experiments were set up against third instar starving larva of Khapra beetle Trogoderma granarium (Everts.) for 24hrs and 48hrs. Results showed that increase in the concentration of botanical synergist significantly increases the toxicity of neem oil. 70% and 50% increases in the percentage mortality of the test organism was observed after 24hrs and 48hrs respectively. Significant decrease in the LD50 was also observed with the increase in the concentration of botanical synergist after 48hrs i.e. 14.71 mg.kg-1 with 0g and 8.65 mg.kg-1, 8.65 mg.kg-1 and 7.65 mg.kg-1 with 2g, 6g and 10g respectively. These results suggest that toxicity of neem oil increases with increase in the concentration of the botanical synergist. Thus, we conclude that Prosopis juliflora used in the present work enhance the toxicity and bioavailability of azadirachtin in neem oil against the target pest and can be used as an efficient substitute for chemical synergist. Hence, this synergistic approach provides an ecofriendly and economically efficient formulation of neem oil for stored grain pest management.