Some biological aspects of Tetranychus urticae Koch on three soybean cultivars (i.e., Giza 21, Giza 35 and Giza 83) at three constant temperatures of 22, 26 and 30°C; 65% R.H. and 16:8 L: D photoperiods were studied. The results indicated that, T. urticae successfully developed on all experimental soybean cultivars at the three constant temperatures. The life cycle of T. urticae was the longest at 22°C followed by 26°C, than 30°C. The longevity of T. urticae female were 18.18, 18.88 and 19.18 days at 22°C, while the shortest periods were 13.65, 13.85 and 15.30 days on Giza21, Giza84 and Giza35, respectively. Significantly differences occurred between all stages at the three levels of temperatures. The highest fecundity and daily rate at 30°C was 95.65 eggs/female and 8.72 eggs/♀/day, while the lowest was71.58 eggs/female and 5.33 eggs/♀/day at 22ºC. Significant differences occurred between the three varieties diets as fecundity was the highest on Giza35 and the lowest on Giza21. These results indicated that, soybean Giza35 was more susceptible to the infestation by spider mite, while Giza21 was more tolerance, whereas Giza83 was in between. The lowest threshold temperature (t₀) to different stages of the mite, T. urticae were recorded as: 14.26, 3.44, 6.34, 11.32, 7.93, 11.32, 9.85 and 4.66 for egg, larva, protonymph, deutonymph, immature, life cycle, generation and life span for the mite females, respectively. Whereas, T. urticae female required 135.4 DDUs to complete its development (egg to adult).