This paper reports the results of an investigation into the effect of Cu additions upon the nano-crystallization behaviour of an Al-Y-Ni alloy. 1 at.% Cu was added to a base alloy of Al₈₈Y₄Ni₈ either by substitution for Al to form Al₈₇Y₄Ni₈Cu₁, or by substitution for Ni to form Al₈₈Y₄Ni₇Cu₁. Consistent with previous findings in the literature, the substitution of Cu for Al was found to increase the thermal stability of the amorphous phase whereas the substitution of Cu for Ni was found to decrease its thermal stability. Comparing the microstructures of these alloys after heat treatment to produce equivalent volume fractions of Al nanocrystals showed average grain sizes of 14 nm, 12 nm and 9 nm for the alloys Al₈₈Y₄Ni₈, Al₈₇Y₄Ni₈Cu₁respectively. The effect of Cu in refining the size of the nanocrystals was attributed to enhanced nucleation increasing the number density of the nanocrystals, rather than diffusion limited or interface limited growth.