Equal channel angular pressing (ECAP) is an important severe plastic deformation process to produce ultrafine grained microstructures in metals and alloys. Magnesium and its alloys generally possess poor workability at temperatures below 250°C. In this thesis, the influence of different passes and processing routes of ECAP on improving the workability and hot deformation behaviour of magnesium alloy AZ31B have been investigated. Workability limit diagrams have been constructed for various processed conditions. Specimens processed by two passes through Route C (Pass 2C) exhibits better workability compared to other passes and the Freudenthal workability criterion is more suitable for prediction of failure in this alloy. Hot deformation behaviour of this alloy has been evaluated as a function of ECAP passes and processing routes using hot compression tests. It was observed that the activation energies for hot deformation decreased after ECAP, and this can be related to the grain refinement due to the ECAP process. Moreover, the influence of ECAP on hot formability of AZ31B magnesium alloy by experimental determination and analysis of processing maps was studied. The presence of dynamic recrystallization offers better workability for the ECAPed alloys compared to the annealed condition.