Five isolates of Azotobacter collected from different regions of Kerala were studied for their survival in rubber (Hevea brasiliensis) plantation soil and for their nitrogen fixing capacity at different pH levels. Only two survived in soil at pH 4.8. One isolate showed more nitrogenase activity from pH 4.5 to 6 and was studied for its effects on growth of rubber seedlings when used in combination with different levels of the recommended dose of urea. The girth of seedlings which received 50 per cent of recommended dose of nitrogen with azotobacter inoculation was comparable to plants which received 100 per cent of the recommended dose alone. Azotobacter inoculation augmented the population of various microorganisms in the rhizosphere of rubber seedlings.