Using 5.4 year Fermi-LAT 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 \sim 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 \sim 1.4 , in the 0.4 to 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 the hadronic origin of the \gamma -rays . The \gamma -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 .