Superplastic behaviour of binary two-phase brass and brasses with aluminium addition are compared. Indicators of the superplasticity are considered at a temperature range of 525–600°C and at constant strain rates of 5·10−4s−1 and 1·10−3s−1. The effect of aluminium addition on the superplastic deformation indicators is studied. Improvement of superplasticity and significant decreasing of cavitation are identified due to alloying by aluminium. Surface relief of the samples after superplastic deformation, and grain boundary sliding contribution are analysed, and deformation mechanisms are discussed.