A roof-side structure includes a roof center rail which is engaged with the bottom surface of a roof panel and one end of which extends to a position of a curtain airbag, a roof rail gusset engaged between a roof side outer reinforcing panel and the one end of the roof center rail, and a side inner panel which is engaged with the roof rail gusset in a state that a curtain airbag is engaged with a front side of the one end of the roof center rail. Accordingly, since the roof rail gusset is arranged inside of the side inner panel so that it does not interfere with the curtain airbag, a layout of the curtain airbag is advantageous. Also, since it is not required to bend the roof rail gusset to connect the roof center rail and the side inner panel, in the event a broadside collision is applied to a vehicle, the roof rail gusset remains unbroken, and thus the rigidity of the roof center rail can be sufficiently reinforced.