The objective of this study was to ,determine trinexapac-ethyl [4-(cyclopropyl- $alpha$ -hydroxy-me-thylene)-3,5-dioxocyclohexanecarboxylic acid ethyl ester] effects on lodging-related traits of rice varieties treated at different application rates and times. Trinexapac-ethyl WP was applied at the rate of 10, 20 and 30g ai/l0a to Heukjinjubyeo and Daeanbyeo, respectively. Effects of trinexapacethyl varied greatly with application time as well as application rate with little differences between rice varieties. As the application rate increased, lodging index, center of gravity and exsertion of panicle above flag leaf decreased, whereas breaking strength and phytotoxicity increased. Exsertion of panicle was greatly influenced by the application time with a little difference by application rate. The most effective application time of trinexapac-ethyl based on lodging index and total internode length (Ist-4th node) was 2DBH(days before heading) in Heukjinjubyeo and 17DBH in Daeanbyeo, resulting in reducing total internode length by 12.9 and 9.7cm, respectively. A significant reduction was found at the 1st, 2nd, and 3rd internodes in Heukjinjubyeo, while at the 2nd and 3rd internodes in Daeanbyeo. No significant difference was found among treatments in the panicle length of both rice varieties but the panicle fresh weights of Daeanbyeo were significantly greater in all trinexapac-ethyl treatments compared with that of the control when measured 20 days after heading. Consequently, trinexapacethyl treatment significantly improved lodging-related traits of rice plants without affecting rice yield and yield components.