Abstract: The property of retarded micro-expansion of MgO hydration products can improve the crack resistance of roller compacted concrete (RCC). Both macro and micro approaches were combined in this work to study the mechanical properties and microscopic morphology of MgO RCC with different MgO contents. An anti-crack coefficient was introduced to evaluate the improvement of crack resistance. The test results show that the MgO additive increases RCC compactness through micro-expansion of Mg(OH)2 and produces an expansion stress that can neutralize the tensile stress caused by temperature drop, and thus it improves the crack resistance of RCC and its mechanical properties.