A novel peptide analog of acylated oxyntomodulin and its uses are disclosed. A pharmaceutical composition containing the novel peptide analog is useful and effective for preventing and treating obesity or overweightness, or diabetes accompanied by obesity and overweightness. The peptide analog and a composition containing the peptide analog are superior to those of wild-type oxyntomodulin in dual agonism on GLP-1 and glucagon receptors and longer in vivo half-life. A pharmaceutical composition containing the peptide analog is effective in the treatment of metabolic diseases such as obesity and diabetes mellitus.