Populations of Tetranychus urticae Koch (Acari: Tetranychidae), and its predatory mite, Agistemus exsertus Gonzalez (Acari: Stigmaeidae), were determined on four soybean varieties during 2016 season, as well as study of some biological aspects for both species was done. The obtained results revealed that Giza 35 variety was the most susceptible variety with significant difference between the mean numbers of T. urticae compared with other varieties. The mean of infestation was 11.89 individuals/25cm² of leaves, while the mean number of T. urticae was 7.11 and 3.54 individuals/25cm² of leaves for Giza 111 and Giza 82 without significant difference. Giza 22 recorded the lowest mean number of T. urticae 1.53 individuals/25cm². The population dynamics of T. urticae cleared that infestation increased gradually from mid-June reach its maximum at the end of July then decreased gradually at the beginning of August reach its minimum number at the beginning of September before the harvest time. As for A. exsertus, data showed that the mean number of A. exsertus was the highest on Giza 35 (2.46 individuals/25cm²) followed by Giza 22 (2.13 individuals/25cm²⁾, but Giza 82 and Giza 111 mean numbers were 1.99, and 1.91 individuals/25cm². Life cycle of Tetranychid males was the shortest when reared on Giza 35with significant difference with other varieties. As for females, the shortest life cycle was when reared on Giza 35 with significant difference with Giza 22, which recorded the longest life cycle for males and females respectively.