Thirty-two diterpenoids were obtained from the root bark of Pinus massoniana, 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 (4) and abieta-8,11,13,15-tetraen-18-oic acid (23) showed moderate phosphodiesterase type 4D (PDE4D) inhibitory effects with IC50 values of 2.8 ± 0.18 and 3.3 ± 0.50 μM, respectively, and their binding modes were investigated by a molecular docking study.