The study of surface reaction controlled growth kinetics of a magnesium sulphate heptahydrate single crystal in [110] direction at T = 15 - 32.5°C and σ = 0.0002 - 0.135 has been performed with the use of interferometric technique. At lower supersaturations the model of dislocation growth fits the experimental data; at higher supersaturations growth is accelerated due to polynuclear two-dimensional nucleation according to the "Birth + Spread" model.