This study is the first transcriptome study for Cd and melatonin treatment in lettuce, both transcriptomes and the expression profile would provide the foundation for further exploring the molecular mechanism of Cd accumulation, and develop breeding strategies aimed at decreasing Cd in crop plants. Overall design: Italian Lettuce (Lactuca sativa L. var. ramose Hort.) seeds were sterilized with 10 % hydrogen peroxide for 10 min and rinsed thoroughly with distilled water for three times, then germinated on moist filter paper in the dark at 20 °C. After the initiation for 0.5 cm, the seeds were transferred to a salver (40 x 30 cm) filled with perlite and covered by vermiculite for moisture holding. Then, they were transferred into the incubator under 23℃/18℃ for 14h/10h in day and night time, respectively. The relative humidity set as 70% and the light intensity was 15,000 lx. After the formation of seedlings, they were watered with 200ml half-strength Hoagland’s nutrient solution per day for 20 days, subsequently cultivated in a growth chamber. 20 days later, the seedlings were divided into two groups: 1) seedlings cultivated with the nutrient solution with 1μmol/L (Sigma-Aldrich, USA) melatonin. 2) seedlings cultivated with the nutrient solution without melatonin. Then, these two groups were treated by 50 μmol/L CdCl2 for simulation a Cd stress environment, and the nutrient solution was replenished regenerated once for three days to maintain constant concentrations. The leaves and root of 0d, 1d, and 5d seedlings in two groups have been sampled, and three biological repeats were included for each treatment . All samples were stored in Ultra-low Temperature Freeze under -80° before conducting.