The present invention relates to pharmaceutical and food compositions for preventing or treating diabetes or obesity, and more particularly to pharmaceutical compositions and functional foods for preventing or treating diabetes or obesity, which contain, as an active ingredient, a novel compound synthesized from a compound separated from an extract of the Stereocaulon alpinum. The novel compounds of the invention have very excellent PTP-1b (protein tyrosine phosphatase-1b) inhibitory activities, act selectively only on PTP-1b among protein tyrosine phosphatases, and are substantial PTP-1b inhibitors which are effective in preventing or treating diabetes or obesity.