Research was done on two important groups of nematodes plant parasitic nematodes and insect parasitic nematodes (entomopathogenic nematodes). Among plant parasitic nematodes root knot nematodes are the most important. It has a wide host range. Tomatoes are the most seriously affected by Meloidogyne incognita. Different varieties were tested against M. incognita for susceptibility, invasion and development of M. incognita. Moneymaker. Titano California, Peelo, Nagina, Riogranade and Pakit were highly susceptible while Fonto, Tamab, Lima, VF-400, PFTO-86 and Samoan were susceptible. Calmart VFN proved resistant. There was a positive relationship between the inoculum level of M. incognita and root weights and inverse relationship with shoot weights. Effect of plant age on plant susceptibility to nematode infection was also studied. Plant extract of neem, onion, garlic, tobacco, aloevera, cloves and chili was investigated for larval mortality and egg hatching of M. incognita. Mortality of nematodes increased with exposure time and extract concentration. Effect of plant extracts on root knot nematodes applied after root knot nematodes and hare dip root treatment was also studied on plant growth parameters plant height, fresh shoot weight, dry shoot weight and fresh root weight. Among all the plant extracts tested neem proved effective followed by onion and tobacco while chili proved less effective as compared to the other plant extracts. In the second part of thesis, effect of entomopathogenic nematodes S. asiaticum, S. glaseri, H. indica and H. bacteriophora on the development of Al, incognita, effect of different inoculum levels, and time of application. live and dead EPN on RKN in addition to the persistence in soil was also studied. Suppression of M. incognita varied with application rate. 'The high application rates of EPN reduced M. incognita infestation as compared to low rates. Reduction in root knot nematode invasion and development was recorded. Numbers of EPN were reduced in non-sterilized soil. Both dead as well as live entomopathogenic nematodes and their material were responsible for lower invasion by M. incognita in tomato.