Guar (Cyamopsis tetragonoloba L.) is used as a food additive, vegetable, and for fuel worldwide. Guar may contain significant concentrations of galactomannan for potential use as a healthy nutraceutical. Ten guar genotypes were selected from the USDA-ARS Plant Genetic Resource Conservation Unit’s collection during 2019. Information for percent galactomannan, seed, and endosperm weight is needed. The overall means for seed and endosperm weight, galactose, mannose, galactomannan %, and the mannose to galactose (M:G) ratio were 33.40 mg, 13.7 mg, 25.23%, 53.26%, 78.03%, and 2.12, respectively. The Congolese and Pakistan genotypes, PI 263406 and PI 262153 produced the highest seed weight averaging 39.77 mg. However, PI 263406 and PI 165511 (India) produced the highest endosperm weight averaging 16.22 mg. Using high performance liquid chromatography (HPLC), the genotypes, PI 263698 (Sudan), PI 253182 (Maryland, USA), and PI 268229 (Iran) were shown to produce the highest mean of 26.5% and 80.33% for galactose and galactomannan, respectively. The Indian genotypes, PI 164299, PI 164477, and PI 263698 produced the highest mean concentration for mannose (54.8%), but it was not significant. The lowest M:G ratios were found in PI 165511, PI 263698, and PI 268229 averaging 2.01 indicating higher solubility. Several correlations were found and both galactose and galactomannan % showed significant negative correlations (r = -0.524* and r = -0.536*, respectively) indicating that galactose and galactomannan % decreased in the seeds stored the longest period (from 12-36 years) at -18 ºC. These results can be used by scientists for guar cultivar development with high galactomannan concentrations.