Red betel leaf (Piper crocatum Ruiz & Pav.) is a plant that has medicinal and cosmetic properties. One of the cosmetics used by society today is facial serum. The purpose of this study was the formulation of facial serum from red betel leaf water extract. The water extract was obtained by means of the Pressurized Hot Water Extraction method using distilled water as a solvent, then phytochemical screening was carried out. Serum is made in several concentrations, namely 1.5% (F1); 2% (F2);3%;(F3) and blank (F0). The quality inspection of the preparation includes homogeneity test, pH, viscosity, stability, irritation test, hedonic test, and antioxidant activity test. The results of phytochemical screening of red betel leaf water extract contained alkaloids, flavonoids, tannins, saponins and triterpenoids. Red betel leaf is formulated into a homogeneous serum preparation with a temporary pH range of 6.1-6.2 after testing has a pH of 5.8-6.1 and does not irritate the skin. The results of the antioxidant activity test showed that the water extract of red betel leaf (Piper crocatum Ruiz & Pav.) was included in the "strong" antioxidant category with an IC50 value of 38.30 g/ml. The IC50 values ​​for serum preparations F0, F1, F2 and F3 were 430.3689 g/ml (weak), 252.03 g/ml (moderate), 115.6 g/ml (moderate) and 58.13 g/ml (strong). Based on this study, it was concluded that all facial serum formulas were homogeneous, stable and did not irritate the skin and serum preparations with 3% red betel leaf water extract (F3) had the best activity in the category of strong antioxidants.