Stereolithography (SLA) is becoming an important fabrication method among the different additive manufacturing techniques. This study investigates the effect of high strain rate on mechanical behavior, considering the fact that materials can be shown different mechanical properties under rapid straining compared to quasi-static loading. In addition, the role of polymerization as a determining factor in the final mechanical properties of the SLA parts is indicated. Regarding that, samples based on urethane dimethacrylate resin material were printed in different directions (θ = [0–90]) and post-treatment was performed with respect to the UV and UV with temperature. The effect of high strain rate was analyzed through a servo-hydraulic machine, monotonic, and interrupted tensile tests ranging from 0.3 to 117.4 s−1. Scanning electron microscopy was applied to analyze the failure surface characteristics. The results show the important effect of strain rate on mechanical properties such that by increasing the strain rate, yield stress and ultimate stress were increased. Furthermore, investigation of the strain rate sensitivity during the different steps of the failure indicates more sensitivity of the non-linear zone of the stress–strain curve with strain rate.