Technical Abstract: A major obstacle to successful cooled semen storage is reactive oxygen species generated in the media by the sperm cells. Recently, many reports document the antioxidant, anti-carcinogenic and anti-mutagenic properties of flavonoids when they were used in vitro or in vivo. Therefore, the objective of this study was to determine whether supplementing diluents with the flavonoids, silibinin or catechin, would aid in maintaining the viability of caprine sperm during cooling and storage at 5°C. Semen samples were collected from seven post pubertal goats using electro-ejaculation and aliquots of sperm (40 x 106 cells), replicated 3 times, were diluted in 9% non-fat dried skim milk extender supplemented with 0 (control), 25, 50, 75, or 100µM of either silibinin or catechin. Diluted samples were cooled and maintained at 5°C prior to microscopic analysis (250x) using a Makler counting chamber. A minimum of 200 sperm cells per sample were counted to determine the percentage of motile sperm at 24, 48, 72 and 96 hours of incubation. An ANOVA was performed on arcsine-transformed data to determine differences in sperm motility between control and treatment levels for each flavonoid. No differences in motility were detected for the silibinin treated samples at any of the concentrations across the four time periods. Significant differences (P < 0.05) in motility were detected between the 0 (control, 34%) and the 25, 50, 75 and 100µM concentrations of catechin (57, 53, 55 and 64% motile cells, respectively) at 96 hours. These results demonstrate that the flavonoid catechin, but not silibinin, aids in maintaining the motility of cooled goat sperm in a dose dependent manner. Theories for the actions of flavonoids on cooled goat sperm are presented.