Rao and Chaturvedi [18] had presented an analysis to consider the effect of thickness on the forming limit diagrams through a correction in the MK model taking into consideration the influence of the triaxial stress state in the neck. This model predicted results closely matching the experimental values for Aluminium which is not sensitive to strain rate. This paper presents a new model for predicting forming limits for strain rate sensitive materials relying on the above work and the approach of Marciniak. Kuczynski and Pokara [13]. The results obtained are found to be in close agreement with experimental values (Pig. 4). The model has also been used to analyse the influence of various material property parameters and thickness on forming limits and these are also found to be in good agreement with reported experimental results. The model has also been extended to predict forming limits under a two stage strain path and the results have been compared with the experimental results of Ishigaki [8] (Figs.11 to 14).