Zn-1.5wt.%Cu peritectic alloy was prepared in a graphite crucible under a vacuum atmosphere. Unidirectional solidification of Zn-1.5wt.%Cu peritectic alloy was carried out with the Bridgman method by using metals of 99.99 % purity under the argon atmosphere and two different conditions; with a temperature gradient (G) range of 1.99-7.81 K mm(-1) at constant growth rate (V) and a growth rate range of 8.41-661.11 mu m s(-1) at a constant temperature gradient. The microstructures of the directionally solidified Zn-1.5wt.%Cu peritectic samples were observed to be cellular. From both transverse and longitudinal sections of the samples, cellular spacing (lambda), and cell tip radius (R) were measured and expressed as functions of solidification processing parameters (G and V) using a linear regression analysis. The experimental results were also compared with values calculated according to the current theoretical and numerical models, and similar previous experimental results.