This study investigated the antioxidant, whitening, and anti-obesity properties of red-fleshed pitaya extracts. We aimed to increase the financial value of red-fleshed pitaya and demonstrate its potential as a functional food material in the future. Flesh and peel extracts were obtained using 70% ethanol and water extraction conditions. Total polyphenol content and antioxidant activity (ABTS and DPPH radical scavenging activity) for each extract were measured, and the 70% ethanol peel extract had the highest total polyphenol content and antioxidant activity. Mushroom tyrosinase inhibitory activity was used to measure the whitening effect, with the water flesh extract being the most effective. To investigate the anti-obesity effect, a 3T3-L1 preadipocyte differentiation experiment was performed at a non-cytotoxic concentration using 70% ethanol and water flesh extracts. In comparison to the control, the water flesh extract showed a substantial decrease in lipid accumulation in a dose-dependent manner. The antioxidant activity of the 70% ethanol pitaya peel extracts and the whitening and anti-obesity effects of the water flesh extracts are expected to make pitaya a highly valuable functional food ingredient.