Glass-ceramics based on nepheline crystal (Na₃(Na,K)[Al₄Si₄O₁₆]) system was modified to satisfy the thermal and optical properties required for a band-pass filter (BPF) in telecommunication systems using optical fibers. The suitable coefficient of thermal expansion was achieved in a glass-ceramic containing more potassium oxide than the conventional nepheline glass-ceramics, in nepheline–kalsilite (K[AlSiO₄]) binary system. An addition of the moderate amount of nucleating agents is a key parameter to obtain high transparency of the glass-ceramics. The optimized nepheline–kalsilite glass-ceramic showed higher mechanical strength as compared with the monolithic glassy material used in the same application.