Objective: To investigate the changes of cyclin L2(CCNL2) gene mRNA and protein during the differentiation of P19 cells to cardiac myocytes, and to explore the relationship between CCNL2 gene and the differentiation of cardiac myocytes. Methods: P19 cells were cultured with 0.9% DMSO for 18 days. Western blots of cardiac troponin I (cTnI) were used to identify cell differentiation. Total RNA was extracted from P19 cells during the process of differentiation at various time points:pre-differentiation(Day 0), and Day 1 to Day 18. The expression levels of CCNL2 gene mRNA and protein were evaluated by RT-PCR and Western blot, respectively. Results: After being induced to differentiate by DMSO for 4 days in suspension, spontaneously and rhythmically beating cells were seen at 8 day, which were cTnI-positive. In P19 cells, both the expression level of CCNL2 gene mRNA and protein were gradually down-regulated. Conclusion: Both the expression of CCNL2 gene and protein were down-regulated during the process of the differentiation of P19 cells into cardiac myocytes, suggesting a possible role for this cyclin in their differentiation．