Two new naphthalenic lactone glycosides, (3S)-9,10-dihydroxy-7-methoxy-3-methyl-1-oxo-3,4-dihydro-1H-benzo[g]isochromene-3-carboxylic acid 9-O-β-D-glucopyranoside (1) and (3R)-cassialactone 9-O-β-D-glucopyranoside (2) were isolated from seeds of Cassia obtusifolia Linn., along with five known compounds: (3R)-cassialactone 9-O-β-D-gentiobioside (3), emodin 1-O-β-gentiobioside (4), 1-hydroxyl-2-acetyl-3,8-dimethoxy-naphthalene 6-O-β-D-apiofuranosyl-(1 → 2)-β-D-glucopyranoside (5), rubrofusarin 6-O-β-D-gentiobioside (6), rubrofusarin 6-O-β-D-triglucoside (7). Structures of 1 and 2 were elucidated by NMR and HR-ESI-MS spectroscopic analysis. Their stereochemistry was determined by CD experiment. All compounds were tested for their ability to inhibit the formation of advanced glycation end-products in vitro. Compounds 1, 2, 3, 5, and 6 showed significant in vitro inhibitory activities (IC values of 11.63, 23.40, 7.32, 89.03, and 38.89 µM, respectively).