The aim of this study was to evaluate the cytotoxic effects of three new butanolides, subamolides A - C (1-3), and a new secobutanolide, secosubamolide (4), on the human colorectal cancer cell line SW480. Compounds 1-4 are new and were isolated from the stems of Cinnamomum subavenium, along with 17 known compounds. The structures of 1-4 were determined by spectroscopic analysis. Propidium iodide staining and flow cytometry were used to evaluate DNA damage of the treated SW480 cells, and it was found that 1-4 caused DNA damage in a dose-dependent manner after 24 h of treatment.