Size　effect,　referring　to　mechanical　properties　of　materials　change　with　the　geometry　changes,　is　the　basic　characteristic　of　brittle　and　quasi-brittle　materials.　Researches　show　that　for　the　concrete　material,　compressive　strength,　split　tensile　strength　and　tensile　strength　decrease　with　the　size　of　components　increases,　for　RC　structures,　size　effect　also　exists.　The　development　and　current　situation　in　size　effect　are　presented　from　three　aspects,　including　concrete,　RC　members　and　the　application　of　the　code.　And　then,　the　developing　trends　of　size　effect　of　RC　members　are　proposed.