Pectin is a class of complex polysaccharides that function as hydrating agents and cementing materials for the cellulose network. Pectin has various health benefits, such as decreasing serum cholesterol levels, alleviating diabetes mellitus, and preventing cancer. It has been reported that the cancer prevention effect is closely related to the structure of pectin (galactose-rich, molecular weight <10,000, and methylation degree 50% to 70%). This study was conducted to investigate the variation of grapefruit pectin content due to harvest time. `Rio Red' grapefruit on sour orange rootstock grown at Texas A&M Univ.-Kingsville Citrus Center were harvested every 2 months and analyzed for pectin content, galacturonic acid concentration, methylation degree, and neutral sugar composition. Results showed that lamella contains more pectin than flavedo and albedo. In the lamella, the edible section, the uronic acid content ranged from 85% to 90% from August to April the following year. Methylation degree increased from August (31.89%) to April (46.99%). Total neutral sugar content of lamella pectin decreased from 110.54 to 61.77% mg·g -1. Galactose, arabinose, and rhamnose are the major sugar contents of pectin (85%), and glucose content increased with the season from 3.14 to 13.34 mg·g-1. Molecular weight of pectin was also determined.