Mature Basella alba L. fruit, with dark blue skin and deep red-violet flesh, is a potential source of natural colorants. Its pigment components and bioactivities deserve particular attention and investigation. In this study, fruit flesh was extracted with 80% methanol (containing 0.2% formic acid) and subjected to solid-phase extraction, semipreparative HPLC isolation, mass spectrophotometric analysis, and structural elucidation. The major red pigment was identified as gomphrenin I. Its quantity increased with the increase of fruit maturity. The gomphrenin I extract yield from ripe fruits was 36.1 mg/100 g of fresh weight. In addition to gomphrenin I, betanidin-dihexose and isobetanidin-dihexose were also detected. The antioxidant activities of gomphrenin I determined by Trolox equivalent antioxidant capacity (TEAC), α,α-diphenyl-β-picrylhydrazyl (DPPH) radical scavenging activity, reducing power, and antioxidative capacity assays were equivalent to 534 μM Trolox, 103 μM butylated hydroxytoluene (BHT), 129 μM ascorbic acid, and 68 μM BHT at 180, 23, 45, and 181 μM, respectively. The anti-inflammatory function was tested at concentrations of 25, 50, and 100 μM in murine macrophages stimulated with lipopolysaccharide (LPS). The results revealed that gomphrenin I suppressed LPS-induced nitric oxide (NO) production in a dose-dependent manner and decreased PGE(2) and IL-1β secretions at the highest concentration tested. The transcriptional inhibitory activities of gomphrenin I on the expression of inflammatory genes encoding iNOS, COX-2, IL-1β, TNF-α, and IL-6 were also observed. It is of merit to identify gomphrenin I as a principal pigment of B. alba fruits and as a potent antioxidant and inflammatory inhibitor. These findings suggest that B. alba fruit is a rich source of betalains and has value-added potential for use in the development of food colorants and nutraceuticals.