Hypaphorine, an a-N,N,N-trimethyltryptophan betaine, is isolated as major constituent from Impatiens niamniamensis seeds (Balsaminaceae) for the first time. The structure of the compound was established by spectroscopic data. This is the first report of its in vivo evaluation for antihyperglycemic activity. The ethanolic extract of the seeds showed mild antihyperglycemic activity at the dose of 200 mg/kg body weight, whereas, hypaphorine showed significant activity in streptozotocin-induced diabetic rats at the dose of 50 mg/kg body weight when compared to standard drug metformin (100 mg/kg).