At the end of 2013, the Hubble Space Telescope has started its last flagship program : the "Frontier Fields". In the framework of this project, three of the most powerful space telescopes to date - Hubble, Spitzer and Chandra - will dedicate a large amount of their observing time to observe six galaxies clusters, who act as additional lenses and amplify the light from background sources, including very faint galaxies to the edge of the observable Universe. These images will reach a depth comparable to the "Hubble Ultra Deep Field", but in a cluster field. Abell 2744, the first Frontier Fields target, has been observed by HST since November 1 and the first release has been made public on December 17. We have used this dataset to search for Lyman Break galaxy (LBG) at z>6.5 in the 4.9 arcmin^2 field of view of the WFC3. Several sources have been selected and the highest redshift object is estimated at z=8, called Abell2744_Y1. The amplification factor of this object is relatively modest (mu=1.5). We used our own reduced Spitzer images at 3.6 and 4.5 microns to constrain the Spectral Energy Distribution (SED) of the z=8 galaxy candidate. We computed its properties by SED-fitting using templates with and without nebular emissions. The star formation rate (SFR) in this galaxy ranges from 8 to 60Mo/yr, the stellar mass is in the order of (2.5-10) x 10^9 Mo and the size r=0.35+/-0.15 kpc, and it is consistent with expectations and previous estimates in this range of redshift. The brightness of this galaxy (F160W=26.2 AB) makes it one of the brightest z=8 object to date, and could be observed by current NIR-spectrograph in a reasonable amount of time.