Composite action between a reinforced concrete deck and steel girders is usually achieved by making use of welded headed shear studs. The mechanics of shear studs embedded in mature concrete has been investigated extensively in the past. Current literature, however, lacks experimental evidence of steel-concrete interface behavior at early concrete ages. This information is useful in understanding the behavior of bridges during construction. Current testing methods are not suitable for determining the response of shear studs embedded in early-age concrete. In order to avoid this limitation, a new pushout test setup has been developed. A total of 24 pushout tests were performed at concrete ages ranging from 4 h to 28 days. Test results were used to develop load-slip curves and strength expressions. Furthermore, the variation of concrete properties with time and the applicability of the existing code equations for predicting early-age concrete stiffness were examined. Test results revealed that shear transfer is achieved at very early concrete ages and rate of stiffness gain of concrete is greater than that of strength.