Pinus morrisonicola Hayata, also known as Taiwan white pine or Taiwan short-leaf pine, is an endemic species to Taiwan. In Asia, particularly Taiwan, China, and Korea, P. morrisonicola needles have been used as a functional beverage for many years. In this study, we investigated the anti-cancer potential of P. morrisonicola leaves and barks against human lung adenocarcinoma (A549) in vitro. Three different extracts, including supercritical CO2 extract, ethanol extract, and steam-distilled essential oils of leaves and barks were obtained. Among them, ethanol extract of P. morrisonicola leaves (PMLE) displayed the strongest cytotoxicity on A549 cells. Next, we found that PMLE treatment arrested lung adenocarcinoma cells induced a pronounced G1/S cell-cycle arrest without triggering apoptosis. Treatment with PMLE resulted in a down regulation of cyclin D1 and phosphorylation of Cdc-2 in A549 cells. In addition, this effect was associated with down regulation of cyclin-dependent kinase 2 (CDK2) and up regulation of CDK inhibitors p21Cip1 and p27Kip1. Moreover, cyclin B1, cyclin D1, and cyclin E expression levels were reduced, which corresponds to a decreased distribution of cells in the S and G2/M phases. Furthermore, PMLE treatment significantly activated p53 in A549 cells, followed by increased nuclear translocation, which may account for the up regulation of p16INK4a, p21Cip1, and p27Kip1 proteins. Taken together, our results indicate that PMLE exerts anti-cancer activity in human lung adenocarcinoma by arresting the cell cycle through activation of the p53-dependent pathway.