This study was conducted at the Horticulture Research Station of Barrage (1999-2000) and (2000-2001) seasons to study the effect of the partial substitution of nitrogen and phosphorus chemical fertilizers with the biofertilizer "Microbein" on yield, fruit quality (weight, firmness, T.S.S., titratable acidity and ascorbic acid %) and fruit chemical constituents (N, P, K) of Camarosa and Oso Grande strawberry cultivars.Morever, to study their susceptibility to infestation by Tetranychus urticae, Bemisia tabaci and Myzus persicae. Each cultivar received five fertilizer treatments [Microbein alone, Microbein + (25, 50 & 75 % of the recommended doses of nitrogen and phosphorus fertilizers (RNPF), and the control (check) one (100 % of the recommended doses of nitrogen and phosphorus without Microbein)              Camarosa cv. gave higher yield than Oso Grande cv.. Data indicated that Camarosa cv. gave higher fruit weight, firmness and titratable acidity and high fruit percentage of phosphorus and potassium. Whereas Oso Grande cv. showed higher values of T.S.S., ascorbic acid and high percentage of nitrogen fruit content.              Results indicated that combined Microbein with 50 and 75 % of the RNPF showed no significant differences on yield as compared as the control treatment during the first season. Whereas in the second season, treatment of Microbein  + 75 %  RNPF showed significant yield increase over the control treatment.Chmical fertilizers combined with Microbein as well as Microbein alone gave similar or even higher fruit weight and firmness during April as compared with the control one. On the other hand, the control treatment showed the highest value of T.S.S. during March 2001.Whereas in April 2001, no significant differences were observed between all fertilizer treatments with regard to fruit titratable acidity and ascorbic acid contents. Nitrogen and phosphorus fruit contents significantly increased with Microbein treatments as compared with the control one. Potassium fruit content was higher in the control treatment than in the other ones.              The treatment of Microbein + 75 % (RNPF) showed the least infestation of the two strawberry cultivars by T. urticae and M. persicae throughout the two seasons followed by the control treatment. The highest infestation was recorded in Microbein treatment alone, while the control was applied for B. tabaci infestation.               Camarosa cv. was characterized by its high infestation with M. persicae, while Oso Grande cv. was more attacked by T. urticae and B. tabaci. The peak infestation with T. urticae was recorded in April, while M. persicae and B. tabaci were in February.