Superplastic behavior of a fine-grained magnesium alloy, ZK61, was investigated at about half the absolute melting point The material was produced by powder metallurgy. The tensile test revealed that the material exhibited superplasticity. The maximum elongation of 659% was obtained at 473 K and 1 x 10(-3) s(-1). Furthermore, it was noted that a large elongation of 283% was attained at a high strain rare of 1 x 10(-2) s(-1). The optimum superplastic strain rate in the present alloy was faster than that in some conventional magnesium alloys, that were shown to exhibit superplasticity at low temperatures. It was suggested that the small grain size increased the optimum superplastic flow in the present alloy.