Various solutions for frequency domain-resource allocation (FD-RA) when frequency hopping is enabled with respect to user equipment and network apparatus in mobile communications are described. An apparatus may determine whether frequency hopping is enabled. The apparatus may determine at least one of a first coarse step size corresponding to a start of an FD-RA and a second coarse step size corresponding to a length of the FD-RA in an event that the frequency hopping is enabled. The apparatus may determine allocated resources blocks (RBs) according to at least one of the first coarse step size and the second coarse step size. The apparatus may perform a transmission on the allocated RBs.