The first results of neutrino oscillation analysis from the Double Chooz experiment is presented. Double Chooz aims to measure theta_13 precisely using two detector sat different baselines, at 400 m (Near Detector) and 1 km (Far Detector). Systematic uncertainties are strongly suppressed by comparing the measurements by the two detectors. Double Chooz started physics data taking by the far detector since April 2011 after the detector commissioning. Neutrino oscillation analysis was carried out using 100 days of physics data. As a result of the analysis using the number of neutrino candidate event and the energy spectrum, deficit of reactor anti-electron neutrino was observed. This deficit indicates the existence of reactor-neutrino oscillation at short baseline as a consequence of non-zero theta_13. This result opens the door to the measurement of CP violation in neutrino sector by next generation neutrino-oscillation experiments.