This paper presents an experimental approach to investigate the long‐term durability of vinyl ester (VE) used in civil/structural engineering. Various alkaline (pH = 7, 11, 12, and 13) and temperature (23, 40, and 60°C) conditions were considered for accelerated aging over 12 months. The test results reveal only slight changes in water absorption capacity (0.75–1.17%) and mass loss (~1%) for the aged VE, which can be explained by the unchanged glass transition temperature. Furthermore, significant hydrolysis reaction and severe microcracking at an elevated temperature resulted in a higher diffusion coefficient. The VE diffusion coefficient increases from 6.60 × 10−7 to 1.75 × 10−6 after 12‐month aging in 23°C water (pH = 7), but becomes 4.00 × 10−6 mm2/s as the water temperature rises to 60°C. Surface microcracks with a depth of ~8.46 μm and chemical hydrolysis reaction with a 74% increment of OH/CH ratio were observed in the 12‐month aged VE at 60°C. However, the diffusion coefficient was insensitive to alkalinity (pH = 7, 11, 12, and 13) regardless of the exposure time and temperatures, which could be attributed to the similar OH/CH ratio at different alkaline conditions. The results of this study shed light on understanding the VE degradation in harsh environments as applied in fiber‐reinforcement polymer (FRP) composites.