Zeolitic imidazolate framework-8 (ZIF-8) is a microporous and crystalline material with strong prospect for many engineering applications. In particular, nanosized ZIF-8 particles with well-defined structure and aperture are highly desirable. In this study, nanosized ZIF-8 particles with narrow and monomodal particle size distribution were successfully synthesized by carrying out the ZIF-8 synthesis in ice bath condition using high concentrations of zinc (Zn2+, 0.20 M) and 2-methylimidazolate (2-mIm(-), 1.60 M) ions. Under low temperature (5 degrees C), ZIF-8 nucleation was enhanced while the subsequent ZIF-8 nuclei growth was suppressed to produce monomodal particle size with mean particle size of ca. 60 nm. The ZIF-8 nanoparticles were also shown to be fully crystalline and possessed proper chemical structure with well-developed pore network as well as good thermal stability up to 200 degrees C.