A method and apparatus are disclosed from the perspective of a UE for requesting SPS resources for V2X message transmissions in a wireless communication system. The method includes generating a first V2X message for transmission. In addition, the method includes transmitting a first signal to a network node for requesting SPS resources for transmitting the first V2X message and V2X messages which are generated subsequent to the first V2X message, wherein the first signal includes an identity used to associate the SPS resources with the first V2X message and the V2X messages. Furthermore, the method includes receiving a second signal from the network node, wherein the second signal contains a first information indicating the SPS resources and the identity. The method also includes transmitting the first V2X message and the V2X messages according to the SPS resources indicated by the first information.