The effect of eight host plants i.e. bean, castor, cotton, jaw's mallow, peanut  , sesame , sweet potato and watermelon leaves of the cotton leaf worm, Spodoptera littoralis larvae on penetration and reproduction of entomopathogenic nematodes Heterorhabditis bacteriophora to S. littoralis larvae were studied under laboratory conditions. The last instar larvae of tested insect were reared on leaves of these host plants under study. Results indicated that the plant on which the host insects fed on significantly affected nematode penetration and reproduction in their larvae with various degrees. In general , the highest number of nematode penetration was recorded in the worms that fed on bean leaves with an averaged 8.33 , 21.33 and 47 IJs/larva at the concentrations of 25 ,50 and 100 IJs / larva, respectively, whereas, the lowest rate of nematode penetration was recorded from the larvae that reared on the jaw's mallow leaves. Meanwhile, the highest averages of nematode reproduction on S. littoralis larvae were produced in larvae that reared on the castor leaves (205400 IJs/cadaver), whereas, reproduction of IJs nematode from larvae which fed on peanut leaves showed the lower number than those of other tested  host  plant leaves.