The amorphous Zr64Ni36, Zr60Ni25Al15, Zr65Ni10Cu17.5Al7.5, and Zr63Ni10Cu17.5Al7.5C2 alloys were successfully synthesized by mechanical alloying of pure element powders. The structural evaluation of powder mixtures in the process of milling was monitored by X-ray diffraction and scanning electron microscopy. The thermal stability of the amorphous alloys obtained and the compositional effects on the glass forming ability were analyzed by differential scanning calorimetry. It was found that, except for Zr64Ni36, other three amorphous alloys exhibit a distinct glass transition and wide supercooled liquid region ranging from 63 to 82 degreesC. The amorphous Zr60Ni25Al15 alloy exhibits the highest glass transition and crystallization temperatures, while the amorphous Zr63Ni10Cu17.5Al7.5C2 phase shows the largest supercooled liquid region. The results demonstrate that addition of appropriate amounts of C extends the supercooled liquid region of Zr-Ni-based amorphous alloys. The effect of the C addition on the glass-forming ability of Zr-Ni-based systems is discussed.