Apparatus and methods are provided for dynamic sidelink (SL) resource allocation. In one novel aspect, one or more uplink (UL) resources are allocated for SL transceiving. In one embodiment, the UE establishes an SL connection with an SL peer UE, receives an allocation indication indicating one or more UL resources are available as shared SL resources for SL transceiving, wherein the allocation indication is originated from a gNB, and performs SL data transceiving with the SL peer UE using the one or more UL resources indicated in the allocation indication. In one embodiment, the UE receives the allocation indication through the Uu connection by unicast, multicast or broadcast. In one embodiment, the shared SL resources are indicated by RB ID or by SL grants. In one embodiment, conditions for using the shared SL resources are included in the allocation indication or are indicated in a separate RRC configuration.