The present work was carried out to study the effect of both temperature and relative humidity on the two spotted spider mite, Tetranychus urticae Koch, Aphis gossypii and Thrips tabaci (Lind) which infesting cotton, Gossypium hirsutum L. at three districts, Abo Kabeer, Belbais and Diarb Nigm in Sharkia Governorate, during the two seasons 2005 & 2006. The obtained data could be summarized as follows: 1. In both seasons, the population of Tetranychus urticae showed two peaks at three districts, recording a highly infestation on the crop at Belbais than that at Abo Kabeer and Diarb Nigm. 2. In both seasons the population of T. tabaci has a one peak at three districts recording 2 highly infestation on the crop at Belbais than the other two districts. 3. The Aphid Aphis gossipii recorded two peaks in both the growing seasons at three districts, showing a highly infestation on the crop at Belbais and Diarb-Nigm than that at Abo-Kabeer. 4. Statistical analysis of the obtained data introduced significant and highly significant correlation coefficient between the population of the two pests T. urticae and Thrips tabaci and both climatic factors and no significant correlation between the population and mean relative humidity except a significant negative correlation between Thrips tabaci during both seasons at Belbais and T. urticae during second season at it district. 5. No significant correlation coefficient between the population of the Aphis gossypii and both climatic factors, except a significant negative difference between A. gossypii with maximum temperature at the second season at Diarb Nigm.