Prunella vulgaris L. (PV) has been used for tumor therapy in Traditional Chinese Medicine for centuries, however, systematic research on extracted PV polysaccharides believed to possess various biological activities, as well as their preventive and anti-tumor effects on lung cancer has not been reported. In this study, two polysaccharides (P31 and P32) were isolated from the aqueous extract of PV and purified through ethanol precipitation, followed by deproteination using DEAE-52 gel-filtration chromatography. The main monosaccharide composition of polysaccharide P32 was analyzed by GC. It was found that polysaccharide P32 consisted of rhamnose, arabinose, xylose, mannose, glucose and galactose in a molar ratio of 3.46:49.32:58.91:0.43:2.64: 3.11, respectively. In order to evaluate polysaccharide P32's anti-lung adenocarcinoma activities and immunomodulation effects, a C57BL/6 mouse-Lewis lung carcinoma (LLC) model was established and investigated. Our results showed that polysaccharides of PV had anti-lung cancer activity and could increase the thymus index and the spleen index in tumor-bearing mice, suggesting possible immunomodulation effects.