The two spotted spider mite (TSM), Tetranychus urticae Koch (Acari: Tetranychidae) is one of the major mite pests on agricultural crops worldwide. The present work aims to study abundance  of TSM and the most common predatory phytoseiid species, Typhlodromips capsicum Mostafa (Acari: Phytoseiidae) on four cotton cultivars viz. Giza 45, Giza 86, Giza 87 and Giza 92 mostly cultivated in Egypt during two successive growing seasons 2016 and 2017 at Aga district, Dakahlia Governorate, Egypt in relation to prevailing atmospheric temperature and relative humidity. Also, the synchronization of TSM and T. capsicum under field conditions on the above-mentioned investigated cotton cultivars was investigated. Obtained results showed that TSM populations were significantly (P≤ 0.05) higher on the cotton cultivars Giza 45 and Giza 92 in comparison with the other investigated ones (Giza 86 and Giza 87) during the two investigated seasons 2016 and 2017. Populations of the phytoseiid species, T. capsicum did not significantly affected by the tested cotton cultivars. There were positive correlations between the changes of TSM and T. capsicum populations and temperature while the correlations with relative humidity were positively insignificant during the two investigated growing seasons. Good synchronization between TSM and T. capsicum populations on tested cotton cultivars was detected during the first and second seasons. These results showed that cotton cultivars, predatory mites and weather factors are of the most important factors affecting the populations of
T. urticae on the investigated cotton cultivars.