Background: Choosing either a mechanical or a bioprosthetic valve during surgical aortic valve replacement (AVR) in middle-aged patients is still controversial, especially with contemporary advancements in valve technology. Aims: To evaluate long-term survival and major morbidity in patients aged 50-70 years undergoing AVR using contemporary mechanical and bioprosthetic valves. Methods: A retrospective study was performed using the TriNetX global database to identify patients aged 50 to 70 years who had primary isolated surgical AVR from 2014 to 2020. Patients who had transcatheter AVR, concomitant, or prior cardiac surgery were excluded. Patients were stratified into 2 groups: mechanical and bioprosthetic. A 1:1 propensity-score matching was performed to control for baseline differences between the two cohorts. The primary endpoint was all-cause mortality and secondary endpoints were stroke, major bleeding, and reoperation over a follow-up period of 8 years. Results: A total of 1,138 propensity-matched patients were included in each group. There was no significant difference in survival, stroke, or reoperation rates between the two groups. Survival probability at the end of the follow-up period was 76.6% in the mechanical group and 80.1% in the bioprosthetic group (HR, 0.946 [95% CI, 0.702, 1.276]) (Figure 1). A total of 137(12%) vs 119 (10.4%) patients had stroke in the mechanical vs the bioprosthetic group, respectively (HR, 1.08 [95% CI, 0.851-1.392]). A total of 19 (1.7%) vs 17 (1.5%) patients had reoperation in the mechanical, and the bioprosthetic valve group, respectively (HR, 1.01 [95% CI, 0.526, 1.951]). There were higher major bleeding events in the mechanical group, 266 (23.4%) vs 163 (14.3%) in the bioprosthetic group, (HR, 1.64 [95% CI, 1.353, 1.999]). Conclusion: Contemporary bioprosthetic valves could be a reasonable option for AVR in patients aged 50 to 70 years with less major bleeding risk and similar survival, stroke, and reoperation rates.