To provide a battery mounting structure of an electric vehicle that can suppress generation of vibrations in a guide of a battery case into a battery case accommodating part even if a positional offset is caused between the battery case and the battery case accommodating part on the side of the vehicle before the battery case is mounted.

The battery mounting structure includes a battery case 20 for storing a battery cell therein, a battery case accommodating part 44 provided in a vehicle body 10A, and a battery case guiding means for guiding the battery case 20. The battery case 20 includes four side faces facing in four directions of front, rear, left and right, respectively, a first corner part having a right angle part formed by two of the side faces, and a second corner part having a right angle part formed by the remaining two side faces. The battery case guiding means includes case side members provided in the side faces on the side of the corner in the first corner part and the second corner part, respectively, and a vehicle body side member that is provided to the vehicle body 10A and can contact the case side member. One of the case side member and the vehicle body side member has a convex curved surface and the other has a tapered surface that can contact the convex curved surface.