Thirty-two diterpenoids were obtained from the root bark of <i>Pinus massoniana</i>, and, among them, five compounds (pinmassins A-E) were identified as undescribed analogues. Spectroscopic methods, X-ray single-crystal diffraction analysis, and ECD calculations were applied to establish the structure of the new isolates. Pinmassin D (<b>4</b>) and abieta-8,11,13,15-tetraen-18-oic acid (<b>23</b>) showed moderate phosphodiesterase type 4D (PDE4D) inhibitory effects with IC<sub>50</sub> values of 2.8 ± 0.18 and 3.3 ± 0.50 μM, respectively, and their binding modes were investigated by a molecular docking study.