Gambir (asen'yaku in Japanese), an aqueous extract of leaves and young twigs of Uncaria gambir Roxb., has traditionally been used as a treatment for diarrhea and dysentery as an internal medicine and for sore throat as a gargle. Although it is a pharmacopoeic medicine in Japan, the quantitative evaluation of its constituents has not yet been adopted in the Japanese pharmacopoeia. We analyzed polyphenolic constituents in 31 gambir and related products to establish evaluation methods, since gambir contains large amounts of polyphenolic constituents. The total flavan contents in the samples revealed using the vanillin-HCl estimation method ranged from 24-79%. Reversed-phase high performance liquid chromatography (RP-HPLC) analysis indicated that catechin was the most abundant constituent in each sample, with contents in the range of 7-76%. The catechin contents in the gambir products between the first and third quartiles were 28-54%. Thus, the lower limit of the catechin content in gambir products can be set at around 20% for quality management. Fifteen tested samples were subjected to HPLC analysis to show the presence of epicatechin (1.5% on average) and the dimeric compounds procyanidin B1, procyanidin B3, and gambiriin A1 (ca. 1% each). The molecular weight distributions of polymeric flavans in the gambir products were analyzed by gel permeation chromatography (GPC) and showed that the average degree of polymerization for each sample was 3 to 7. These results indicate that the combination of the vanillin-HCl method, RP-HPLC analysis, and GPC analysis gives valuable information for evaluating the polyphenolic profiles of gambir products.