Al-5 wt.% Zn samples were prepared using high purity (99.99%) metals in graphite crucibles. The samples were directionally solidified upward with a constant temperature gradient (G = 5.5 Kmm(-1)) and different growth rates, V, (8.25-165 mu m/s) in a Bridgman type directional solidification apparatus. The dendritic spacings (lambda(1): Primary dendrite arm spacing, and lambda(2): Secondary dendrite arm spacing) were measured from the longitudinal sections of the samples and lambda(1) was also measured from the transverse sections. The measured spacings were expressed as functions of the growth rates by using a linear regression analysis. The effect of V on lambda(1) and lambda(2) were investigated. The experimental results were compared with the results of the current theoretical and numerical models and similar previous experimental results.