The present invention relates to a novel peptide showing more excellent activities on a glucagon like peptide-1 receptor and a glucagon receptor than native oxyntomodulin, and a composition for the prevention or treatment of obesity comprising the peptide as an active ingredient. Unlike native oxyntomodulin, the novel peptide of the present invention reduces food intake, suppresses gastric emptying, and facilitates lipolysis with reduced side-effects, and also shows excellent receptor-activating effects. Thus, it can be widely used in the treatment of obesity with safety and efficacy.