The cosmetics industry expects low irritation and skin improvement effects by utilizing natural ingredients and botanical extracts. In particular, Poncirus trifoliata fruit extract is a traditionally recognized ingredient with proven pharmacological efficacy and contains various bioactive compounds. According to previous studies, Poncirus trifoliata fruit has been reported to possess antioxidant, whitening, and skin-improving effects. In this study, the antioxidant and whitening efficacy of Poncirus trifoliata fruit extract was evaluated according to different extraction solvents, and the formulation stability of a cleanser containing this extract was analyzed. The antioxidant activity of Poncirus trifoliata fruit extract was confirmed by measuring DPPH and ABTS⁺ radical scavenging activity, while its whitening efficacy was assessed through tyrosinase inhibition activity. Additionally, the total polyphenol and flavonoid content was measured, confirming its strong antioxidant effects. These findings suggest that Poncirus trifoliata fruit extract may contribute to anti-aging and skin-whitening effects. To evaluate the stability of a cleansing formulation containing Poncirus trifoliata fruit extract, pH and viscosity changes were measured over 28 days under temperature conditions of 5°C, 25°C, and 45°C. The results indicated a decline in stability over long-term storage. Therefore, further studies are required to optimize the extract concentration and improve the formulation for enhanced long-term stability. This study suggests that Poncirus trifoliata fruit extract has potential as a functional cosmetic ingredient for skin whitening and anti-aging and can serve as fundamental data for future research on stability enhancement.