SummaryThis letter presents the design of digital fractional‐order Butterworth filter (DFOBF) of order (n+α), where n is an integer, and α ∈ (0,1), from the perspective of optimal realization. The magnitude–frequency characteristic of the DFOBF is optimally modeled using the computationally efficient lattice wave digital filters (LWDFs). Design examples for the third‐ and fifth‐order LWDF‐DFOBFs with various values of n, α, and cut‐off frequencies are presented.