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Al-4.95% Zn alloy is directionally solidified in a modified Bridgman apparatus with higher temperature gradient to investigate response of cellular/dendritic microstructures and primary spacing to the variation of growth velocity under near-rapid directional solidification condition. The results show that, with increasing growth rate, there exists a transition from dendrite to fine cell and a wide distribution range in primary cellular/dendritic spacing at the given temperature gradient. The maximum, λmax, minimum, λmin, and average primary spacing, (-λ), as functions of growth velocity, v, can be given by λmax = 12 340 v-0.8353, λmin = 2953.7 v-07717, (-λ)= 7820.3 v-08333, respectively.