Using 5.4 yr Fermi Large Area Telescope data, we report the detection of GeV. gamma- ray emission from the shell-type supernova remnant RCW 86 (G315.4-2.3) with a significance of similar to 5.1 sigma. The data slightly favors an extended emission of this supernova remnant. The spectral index of RCW 86 is found to be very hard, Gamma similar to 1.4, in the 0.4-300 GeV range. A one-zone leptonic model can well fit the multi-wavelength data from radio to very high energy gamma-rays. The very hard GeV gamma-ray spectrum and the inferred low gas density seem to disfavor a hadronic origin for the gamma-rays. The. - ray behavior of RCW 86 is very similar to several other TeV shell-type supernova remnants, e. g., RX J1713.7- 3946, RX J0852.0-4622, SN 1006, and HESS J1731-347.