Vat-photopolymerization (VPP) is a photo-curing-based additive manufacturing (AM) technology for generating nanoparticle-reinforced photopolymer composites. It can also produce specimens with greater geometrical precision and a decent surface appearance. This study uses VPP based on Digital Light Processing (DLP) technique to fabricate the photopolymer composites and analyze mechanical properties. As a nanofiller, Alumina was added to the photopolymer at a concentration of 1 wt% and the test pieces were printed at four different layer thicknesses, namely 35, 50, 75, and 100 µm. To illustrate the effect of alumina nanoparticle fillers in the neat photopolymer at varied layer thicknesses, tensile strength and Young’s modulus values were analyzed. It was discovered that thinner layers offered more tensile strength and Young’s Modulus. This impact was even more substantial in the alumina/photopolymer composite specimen. Furthermore, using alumina nanoparticles improved the composite’s yield strength and Young’s Modulus.