Three chemical synthesis approaches were developed to obtain binary solid solution Bi-Sb nanoparticles (NP) with controllable compositions and sizes. In each synthesis approach, an array of Bi-100-Sb-x(x) NPs with x ranging from 25 to 90 was synthesized via careful control of feeding ratios and synthetic conditions. The NP sizes can be varied from 30 to 60 nm for single-crystal NPs, and from 350 to 500 nm for polycrystal NPs. The synthesized Bi-100-Sb-x(x) NPs can be used as thermoelectric materials or as seeds for growth of ternary solid solution Bi-Sb-Te NPs with different compositions.