Objective To observe endothelial progenitor cells (EPCs) participating in the formation of neovascularization in lung adenocarcinoma. Methods EPCs were transfected by recombinant adenovirus carrying LacZ gene in optimal transfection concentration, and then EPCs were injected into animal models of lung adenocarcinoma through the tail vein; afterwards, lung tissues were taken out for pathological examination in the 6th, 7th, 8th week respectively. EPCs were observed to take part in the angiogenesis in the lung adenocarcinoma through X-gal chromogenic dye. Results The optimal multiplicity of infection (MOI) of AD5F35LacZ transfected EPCs was 400. When MOI was 400, maximum transfection efficiency was 97.13±2.08. After 2 weeks, LacZ gene-transfected EPCs began to proliferate in vitro culture, then the EPCs were transplanted into animal models of lung cancer to be involved in the neovascularization formation in the 8th week after transplantation. Conclusion EPCs are involved in the formation of tumor neovascularization after transplantation.