Abstract: An experiment to study the effect of cutting heights on yield and nutritive values of King napier grass (Pennisetum purpureum cv. King grass) was conducted on sandy loam, Korat soil series (Oxic Paleustults) under irrigation during June 2006 to November 2007 at Khon Kaen Animal Nutrition Development Research Center, Thailand. Four treatments of cutting height at 0 (T1), 5 (T2), 10 (T3) and 15 (T4) cm above ground level in randomized complete block design with 4 replications were employed. The results showed that the Total Dry Matter Yield (TDMY) and Average Dry Matter Yield (ADMY) (65,707.5, 67,070.0, 69,697.5 and 71,403.1 kg/ha/year ; 5,973.4, 6,096.4, 6,336.2 and 6,491.2 kg/ha/cut, respectively) were significantly higher (p<0.05) in T4 than T1. There were no significant differences in CP and DMD among treatments, ranging from 12.1-12.9 and 75.5-76.6%, respectively but the percentage of ADF, NDF and ash were highly significantly different (41.7-43.5, 64.6-66.2 and 13.1-14.7%), respectively. Based on this research, it can be concluded that cutting height can affect the forage DM yield and nutritive values of King Napier grass. Cutting 35 day interval at 15 cm height above ground level could be the optimal level for harvesting King Napier grass in Northeast of Thailand.