The crystallization behavior in the $Al_{87}Ni_3Y_{10}$ and $Al_{88}Ni_3Y_9$amorphous alloys has been investigated. As-quenched $Al_{87}Ni_3Y_{10}$ amorphous phase decomposes by simultaneous formation of Al and intermetallic phase at the first crystallization step, while as-quenched $Al_{88}Ni_3Y_9$ amorphous phase decomposes by forming Al nanocrystals in the amorphous matrix. The density of Al nanocrystals is extremely high and the size distribution is homogeneous. Such a microstructure can result from rapid explosion of the nucleation event in the amorphous matrix or growth of the preexisting nuclei embedded in the as-quenched amorphous matrix. The final equilibrium crystalline phases and their distribution at 873 K are exactly same in both $Al_{87}Ni_3Y_{10}$ and $Al_{88}Ni_3Y_9$ alloys.