The present invention relates to mouse antibodies that bind to angiopoietin-2 (Ang2), humanized anti-Ang2 antibodies derived therefrom, and the use thereof. The anti-Ang2 antibodies have a dual function of activating the Tie2 receptor together with neutralizing Ang2. The anti-Ang2 antibodies show the property of normalizing abnormal and pathological blood vessels, and thus exhibits therapeutic efficacy against various diseases and disorders associated with abnormal blood vessels. The present invention further provides an angiogenesis inhibitor and a composition for treatment of diseases associated with abnormal Ang2 expression and Tie2 dysregulation, which comprise the antibody as an active ingredient, and a composition for diagnosing diseases associated with Ang2 inhibition and Tie2 activation, which comprises the antibody.