A pillar garnish fixing structure comprising: a pillar garnish; a body having a clip fixing aperture having a diameter; and a clip, made from a resin having an elasticity, for fixing the pillar garnish to the body, the clip comprising: a seat; a hollow shaft extending away from the seat and having an interior space opening to an outside at an opposite seat-side end of the shaft; and a pair of engagement hooks opposing each other, each of the pair of engagement hooks being connected to the shaft at a hook connecting portion located at an opposite seat-side end of the engagement hook, being separated from the shaft and the seat by a slit except for the hook connecting portion, and extending from the hook connecting portion toward the seat, characterized in that a distance (d) between outside surfaces of the pair of engagement hooks at the hook connecting portions, located at the same axial position as an opposite seat-side end of the slit, in a free state of the clip is larger than the diameter of the clip fixing aperture of the body, a deformation promoting portion, for promoting the hook connecting portion and a hook root portion connected to the hook connecting portion to be deformed in a direction toward a center axis line of the clip when the shaft is inserted into the clip fixing aperture formed at the body, is formed at each of a pair of shaft wall portions opposing each other in a diametrical direction perpendicular to a direction in which the pair of engagement hooks are opposed, the deformation promoting portion being constructed of at least one of an elongated aperture and a wall thickness decreased portion, and the deformation promoting portion extends in an axial direction of the shaft and in opposite directions away from a position of the shaft corresponding to the hook connecting portion in the axial direction of the shaft. a pillar garnish; a body having a clip fixing aperture having a diameter; and a clip, made from a resin having an elasticity, for fixing the pillar garnish to the body, the clip comprising: a seat; a hollow shaft extending away from the seat and having an interior space opening to an outside at an opposite seat-side end of the shaft; and a pair of engagement hooks opposing each other, each of the pair of engagement hooks being connected to the shaft at a hook connecting portion located at an opposite seat-side end of the engagement hook, being separated from the shaft and the seat by a slit except for the hook connecting portion, and extending from the hook connecting portion toward the seat, characterized in that a seat; a hollow shaft extending away from the seat and having an interior space opening to an outside at an opposite seat-side end of the shaft; and a pair of engagement hooks opposing each other, each of the pair of engagement hooks being connected to the shaft at a hook connecting portion located at an opposite seat-side end of the engagement hook, being separated from the shaft and the seat by a slit except for the hook connecting portion, and extending from the hook connecting portion toward the seat, characterized in that a distance (d) between outside surfaces of the pair of engagement hooks at the hook connecting portions, located at the same axial position as an opposite seat-side end of the slit, in a free state of the clip is larger than the diameter of the clip fixing aperture of the body, a deformation promoting portion, for promoting the hook connecting portion and a hook root portion connected to the hook connecting portion to be deformed in a direction toward a center axis line of the clip when the shaft is inserted into the clip fixing aperture formed at the body, is formed at each of a pair of shaft wall portions opposing each other in a diametrical direction perpendicular to a direction in which the pair of engagement hooks are opposed, the deformation promoting portion being constructed of at least one of an elongated aperture and a wall thickness decreased portion, and the deformation promoting portion extends in an axial direction of the shaft and in opposite directions away from a position of the shaft corresponding to the hook connecting portion in the axial direction of the shaft.