A connection structure may include at least one of left/right front pillars and a cowl, wherein the cowl may include a lower cowl having a body plate extended in a width direction of the vehicle and defining a lower portion of the cowl and a first flange, and an upper cowl covering an upper portion of the lower cowl, wherein the front pillar includes an inner front pillar forming an inner side portion of the front pillar in the width direction of the vehicle, and an outer front pillar forming an outer side portion of the front pillar in the width direction of the vehicle, and wherein the lower cowl is fixedly coupled to the front pillar by at least one inner side surface of the body plate and the first flange contacting an outer side surface of the inner front pillar.