To provide an engine room side part structure capable of covering and closing a gap between a fender panel and a side wall member of an engine room.

This engine room side part structure 100 in a vehicle 102 including the fender panel 112 to be the exterior in the vicinity of a front wheel and having a boundary L1 between the fender panel 112 and a front hood 104 on a side surface includes: cowl side panels 108 on both sides of a vehicle width direction of an engine room 107; a cowl top garnish 101 mounted between upper faces 110 of the cowl side panels 108; and a cover part 118 extending from an end part 119 of the cowl top garnish 101 toward an upper edge 120 of the fender panel 112 at the vehicle outside of the cowl side panel 108 and covering and closing the gap E1 between the cowl side panel 108 and the fender panel 112.