Crisphead lettuce is one of the main vegetables in the world. This crop has the potential for export in Taiwan. The harvest season of crisphead lettuce is from November to March. Most varieties are lack of heat resistance. In this study the yield and heat tolerance of 12 lettuce varieties (lines) were investigated during September to November, 2009 in XinHua, Baojhong and Mailiao. The results showed that the weight and head size 'Chang Lee No. 3' and 'Acacia Dan No. 10' were similar to 'No. 3'. This two cultivars could be introduced for early season.