The present study was conducted at Sakha Agricultural Research Station, Kafr El—Sheikh governorate, Egypt during 2016 and 2017 late cotton seasons. Results showed that Ethephon (plant growth regulator) treatment gave the highest reduction percentage, 56.68 and 37.60% of pink bollworm infestation, Pectinophora gossvpiella (Saund.) with 3 cm3/L, while they were 50.66 and 43.75% of spiny bollworm infestation, Earias insulana (Bois.) with 1.5 cm³/L in 20l6 and 2017 cotton growing seasons, respectively. On the other hand, concentration of Ethephon, 2.5 cm³/L gave the highest increasing of percentages of mature boll opening recording 36.68 arid 22.57% in the two tested seasons respectively, It could be concluded that using Ethephon with 3.0 cm³/L to accelerate mature boll opening in late cotton season.