Arbitrary ratio sampling rate conversion (SRC) structure using B-spline interpolation is proposed for software defined radio (SDR) in this paper. By combining SRC with SDR’s transmitter/receiver filter, the constraint on SRC reconstruction filter can be relaxed, and an overall computational reduction can be achieved. The mixed-width B-spline is introduced so that both antiimaging and anti-aliasing requirements for SRC are satisfied. The passband droop introduced by the B-spline interpolation is compensated by a linear phase digital filter incorporated in the SRC structure so that the overall frequency response approaches the desired frequency response of the SDR’s transmitter/receiver filter. To make the proposed SRC structure applicable in practice, the mixed-width B-spline is further converted into uni-width B-spline, and the simplified implementation of the uniwidth B-spline interpolation is also derived. A design example of the linear phase digital filter for the proposed SRC structure is given for an IEEE 802.11g wireless local area network (WLAN) SDR receiver, and the overall SRC complexity is analyzed.