Abstract: This study investigated the changes in acid invertase activity and sugar contents in lettuce (Lactuca sativa L. cvs. ‘Shizuka’ and ‘Shisuko’) during storage at 20°C. Percent weight loss of the heads was highest after 2 days of storage. In both cultivars, the degree of greenness continuously declined with time. Respiration rate decreased in ‘Shisuko’, whereas the rate in ‘Shizuka’ increased at the end of storage. The activity of acid invertase in soluble and cell wall-bound fractions decreased with few fluctuations throughout the storage period in both cultivars and portions. The acid invertase in the cell wall-bound fraction showed a higher activity than the soluble fraction. The soluble sugar contents gradually decreased in both cultivars and portions as storage progressed. Fructose content was higher than glucose and sucrose in the leaves of two cultivars. In the leaves of ‘Shisuko’, there was a significant positive correlation between the acid invertase activity and the soluble sugars. Comparing the two cultivars, #Shisuko’ showed higher percentage of weight loss, degree of yellowing, respiration rate and has low sugar contents than ‘Shizuka’.