This work was carried out at private farm (loamy soil), in Shobramant village, Giza governorate., during 2005 and 2006 summer  planting seasons, to evaluate effect of reducing the recommended dose of nitrogen and phosphorus mineral fertilizers combined with seed potato tubers and plant inoculation with bio-fertilizers  on plant growth, productivity, tuber quality expressed as nitrate and nitrite accumulation, specific gravity, dry matter and total carbohydrate of two potato cultivars and bacterial densities (total count of microbes, number of Azotobacter spp., number ofAzospirillum spp.in the rhizosphere.  The results showed that Diamant and Spunta cultivars differed significantly in their responses to growth, yield and tuber quality characteristics, Spunta cultivar recorded the best growth with highest mean tuber weight, nitrate and nitrite tuber content. Reducing mineral N, P levels to 90, 80 and 70 % of the recommended rates combined with bio-fertilizer gave equal yield to that obtained by recommended doses. Moreover, reducing mineral N, P levels to 60 and 50% of the recommended rates significantly increased tuber specific gravity and reduced nitrate and nitrite accumulation in potato tubers. The most promising treatment is bio-fertilizer combined with 70% of recommended mineral N, P dose which satisfy the objective of producing high quality tuber with low nitrate and nitrite level and save about 30% of the cost of nitrogen and phosphorus fertilizers. On the other hand, microbial of densities of bacterial counts, azotobacter, azospirilla and bacillus in the rizosphere increased gradually with advanced reducing mineral fertilizers. Reducing mineral NP rates to the half and biofertilizer produced high  quality tubers with low nitrate and nitrite content and also increased microbial densities in potato root rhizosphere.