Abstract: This study is to investigate the expression of CyclinD1 in asthmatic rats and construct expression plasmids of sense and antisense CyclinD1 gene and transfect them to asthmatic airway smooth muscle cell to study the effects of CyclinD1 on the proliferation of airway smooth muscle cells in asthmatic rats. CyclinD1 cDNA was obtained by RT-PCR of total RNA extracted from the airway smooth muscle in asthmatic rats. The sequence was inserted into eukaryotic expression vector pcDNA3.1(+) to recombinate the sense and antisense pcDNA3.1-CyclinD1 eukaryotic expression vector. The two recombinations and vector were then separately transfected into airway smooth muscle cell in asthmatic rats by using liposome. The expression level of CyclinD1 was certificated by Western blotting analysis. The proliferations of ASMCs isolated from asthmatic rats were examined with cell cycle analysis, MTT colorimetric assay and proliferating cell nuclear antigen (PCNA) immunocytochemical staining. Results showed (1) Compared with control group, the content of CyclinD1 was significantly increased; (2) It was comformed by restriction endonucleasa digestion and DNA sequence analysis that the expression plasmid of sense and antisense CyclinD1 were successfully recombinated. There was significant change of CyclinD1 expression between vector and sense CyclinD1 transfected cells, and the expression level of CyclinD1 in ASMC transfected with antisense CyclinD1 was lower than that in vector transfected cells (P<0.01); (3) In the asthmatic groups, compared with the vecter group, the percentage of S+ G₂M phase, absorbance A value of MTT and the expression rate of PCNA protein in ASMC transfected with pcDNA3.1-CyclinD1 vector significantly increased. The values decreased remarkably in the pcDNA3.1-asCyclinD1 group. Statistical analysis revealed that there were significant differences in these indicators of cell proliferation in three groups (P<0.01). In the normal groups, statistical analysis revealed that there were significant differences in the percentage of S+G₂M phase, a value of MTT and the expression rate of PCNA protein in three groups (P<0.01). Sense CyclinD1 eukaryotic expression vectors could have a positive effect on the proliferation of ASMC, however the antisence one have a negative effect, which implicated that CyclinD1 might contribute to the process of airway smooth muscle cell proliferation.