  We study gamma-ray line signatures from electroweakly interacting non-abelian
spin-1 dark matter (DM). In this model, $Z_2$-odd spin-1 particles including a
DM candidate have the SU(2)$_L$ triplet-like features, and the Sommerfeld
enhancement is relevant in the annihilation processes. We derive the
annihilation cross sections contributing to the photon emission and compare
with the SU(2)$_L$ triplet fermions, such as Wino DM in the supersymmetric
Standard Model. The Sommerfeld enhancement factor is approximately the same in
both systems, while our spin-1 DM predicts the larger annihilation cross
sections into $\gamma \gamma/ Z \gamma$ modes than those of the Wino by
$\frac{38}{9}$. This is because a spin-1 DM pair forms not only $J=0$ but also
$J=2$ partial wave states where $J$ denotes the total spin angular momentum.
Our spin-1 DM also has a new annihilation mode into $Z_2$-even extra heavy
vector and photon, $Z' \gamma$. For this mode, the photon energy depends on the
masses of DM and the heavy vector, and thus we have a chance to probe the mass
spectrum. The latest gamma-ray line search in the Galactic Center region gives
a strong constraint on our spin-$1$ DM. We can probe the DM mass for $\lesssim
25.3~$TeV by the Cherenkov Telescope Array experiment even if we assume a
conservative DM density profile.
