  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 $\sim5.1\sigma$. The data slightly favors an extended emission
of this supernova remnant. The spectral index of RCW 86 is found to be very
hard, $\Gamma\sim1.4$, 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.
