A new diterpenoid, 15,16,17-trihydroxy,18-carboxylic acid 18-neo-clerodan-3,13-(Z)-diene was isolated from Sheareria nana S. Moore. The structure was elucidated by spectroscopic data. Compound 1 was evaluated for cytotoxic activities against human endometrial carcinoma cells (ECC-1). The results indicated that 1 showed moderate cytotoxic activity against ECC-1 cell lines with IC50 values of 5.6 ± 0.3 and 2.2 ± 0.2 μM for 24 and 48 h, respectively. Taken together, 1 was a good choice for the treatment of endometrial carcinoma. [ABSTRACT FROM AUTHOR]