A vehicular canister mounting structure includes a vehicle body floor provided on rear frames, a canister being provided underneath the vehicle body floor for treating gasoline vapor produced within a fuel tank, a guide pipe for protecting the canister, and a support for supporting the guide pipe and the canister on a vehicle body. The support includes a guide pipe bracket welded to the vehicle body floor for supporting the guide pipe, and a canister bracket welded to the guide pipe bracket for supporting the canister. Strength with which the canister bracket is welded to the guide pipe bracket is smaller than a strength with which the guide pipe bracket is welded to the vehicle body floor.