Аннотация:We considered the origin and evolutionary conditions for the axial magma chamber (AMC) in the rift zone of mid-oceanic ridges (MOR), in the framework of the continuous-discrete spreading model. Calculations show that the depth to the chamber top depends on spreading rate, periodicity of the tectono- magmatic cycle, fracturing in the crust, hydrothermal activity and thermophysical properties of MOR rocks. Numerical modelling suggests that the quasi-stationary AMC structure in the axial MOR zone likely does not exist if the spreading rate is less than 3 cm yr-1. At greater spreading rates this structure is developed in the crust of axial MOR zone over a period of 150,000-200,000 years. Analysis of evolution of the AMC chamber shape on its cooling stage demonstrates that an interruption between the periodic intrusions of more than 100,000 years results in the disappearance of the magma chamber.