Ethylene plays an important role in fruit ripening and square and boll abscission in cotton. Ethylene also mediates in the senescence process as an accelerator in which cells undergo programmed cell death induced by developmental and environmental signal. This study invested the physiological effects of ethylene inhibiting compound 1-methycyclopropene (1-MCP) on cotton plants under controlled environment by membrane leakage method. Cotton plants were exposed to 1-MCP treatment at early square stage. The method of using electrolyte leakage to estimate the 1-MCP effect on cotton cell membrane stability was optimized first. 7-min wash to remove surface adhering residues was needed and 1h was sufficient time to incubate leaf disks in water. The most effective 1-MCP rate was determined as 12.5 g ai/ha on cotton plants under normal condition. The protection effect of 1-MCP against membrane damage was found on older leaves (leaf position 5^th and 6^th rather than 2^nd, 3^rd, and 4^th), indicating 1-MCP could lower the stress level caused by aging. 4 h was needed for 1-MCP take effect on membrane stability.