Abstract: To study the changes of cortical cytoskeletal proteins of Tetrahymena thermophila, we used the cells of mating type-Tetrahymena thermophila BF1 and BF5. When mixed, the cells underwent a sexual phase involing conjugation. The conjugation course was divided into four important phases in accordance with the changes of cellular nucleuses and their form with microscopic examination. Cortical cytoskeleton proteins had been prepared by biochemical extraction with Tritonx-100, SDS-PAGE and scan. The data statistics had been analyzed by a computer. The results showed that 55KD, 52 5KD, 49KD and 225KD, 150KD, 130KD decreased during conjugation. The 80KD, 87KD, 88KD only appeared in vegetation and early of conjugation, but 90 5KD, 85 5KD and 66KD appeared in the whole conjugation course. These proteins were involved in cortical reorganization during conjugation. They also had some connections with the meisosis of small nucleus and the formation of conjugation fileds.