The Aphis gossypii Glover is an important pest of Bt cotton. We determined the toxicity of the primary and secondary forms of Photorhabdus luminescens (Thomas and Poinar) isolated from entomopathogenic nematode Heterorhabditis indica against A. gossypii. The treatment included different concentration (101 to 1010cells/ CFS/ml) cells and cells free supernatant which was obtained by centrifugation (4000 rpm for 20 min) of broth culture. The treatment were imposed through potter’s tower on aphid colony containing of 20 per leaf/ replication.observation of aphid mortality was recorded at 24, 48 hr and the data was subjected to ANOVA and probit analysis. The results revealed that both the forms were toxic to A. gossypii resulting in significant nymphal mortality within 24-48 hr. The CFS of both primary and secondary forms at the highest concentration of 1010 CFS were significantly more toxic than the cells, resulting in 100 per cent mortality within 48 hr. At the same concentration and exposure time the primary form cells recorded 77.50 per cent mortality and secondary form cells has recorded 83.75 per cent mortality. However, the per cent mortality decreased with the decrease in the cells and CFS concentration. The LC50 varied for cells and CFS of both the forms and with the exposure time. At 48 hr, primary form cells and CFS recorded the LC50 of 1.00 × 105 cells/ml and 2.02 × 102 CFS against aphid, respectively. Whereas, secondary form cells and CFS has recorded LC50 of 1.67× 105 cells/ml and 2.27× 103 CFS respectively. These results indicate the possibility of using P. luminescens in the integrated management of A.gossypi Bt cotton.