Objective To study the main subtypes messenger ribonucleic acid（mRNA） and the basal enzyme activity of phosphodiesterase (PDE) in rat pulmonary microvascular endothelial cells (PMVECs） through the examination mRNA expression and activity of PDE EM>in vitro/EM>. The data were offered to reveal the relationship between PDE distributions, activity change and to accumulate data for the possibility of drug regulation of its functional alteration. Methods The cells were cultured with tissuesticking method; the gene expression of PDEs was detected by reverse transcript polymerase chain reaction (RT-PCR), and the activity of PDEs was calculated by cyclic nucleotides content change examined with high performance liquid chromatogram (HPLC) before and after the PDE reaction（EM>n/EM>＝3）. Results The PMVECs identified by cell immunofluorescence with polyclonal antibody of CD31 were dissociated and cultured, mRNAs of PDE1A, 1C, 2A，3A, 3B, 4A, 4D, 5A, 7A, 7B, 8A, 8B, 9A, 10A,11A were expressed in PMVECs, but there was no mRNA of PDE1B expressed in PMVECs. cAMP/cGMPPDE in the extent of 5-20μl had a