Garcinia mangostana L. is a tropical fruit increasingly consumed in Cameroon, while its kernels are generally discarded as waste. This study evaluated mangosteen kernels as a potential functional ingredient for preventing and managing cardiometabolic diseases. Kernels were isolated, cleaned, sliced, freeze-dried, and powdered. Mineral composition was determined by atomic absorption spectrophotometry. Bioactive compounds were extracted using distilled water, hydroethanol (70:30, v/v), and ethanol and quantified spectrophotometrically. Antioxidant activity was assessed using DPPH radical scavenging, ferric-reducing power, and total antioxidant capacity (TAC) assays. The kernels contained high levels of calcium (471.05 mg/100 g DM) and magnesium (162.79 mg/100 g DM), while zinc reached 1.82 mg/100 g DM and potassium occurred in trace amounts. Ethanolic extract exhibited the highest total polyphenol (194.11 ± 0.66 mg GAE/g DM) and alkaloid (4.77 ± 0.05 mg QuiE/g DM) contents, whereas aqueous extract showed the highest flavonoid content (1.69 ± 0.11 mg QE/g DM). Hydroethanolic extract displayed the strongest DPPH scavenging activity (59.90%), ferric-reducing capacity (179.538 mg AAE/g DM), and TAC (1.318 mg AAE/g DM). Principal component analysis indicated that antioxidant activity was associated primarily with extraction solvent. These findings highlight mangosteen kernels as a promising source of minerals and bioactive compounds.