Experiments were carried out to study the decay characteristics of non-circular supersonic jets issued from rectangular and elliptical nozzles, and results were compared with circular case. Numerical simulations and Schlieren image study were carried out to validate the experimental results obtained from total pressure data. The supersonic core lengths of the jets were found to be different for different exit shaped geometries and area ratio for those nozzles was same. To avoid the losses in divergent section, the shape of cross-section of throat was maintained same that of as the exit. The exit shape geometry played the important role to enhance the mixing of the jet with ambient air, without requiring secondary method to increase the mixing characteristics. The mixing with ambient air in case of non-circular jets was more intense when compared to that of circular jets, which resulted in reduction of supersonic core length. The behavior of supersonic core length had identical signature for both under-expanded and over-expanded operation. The supersonic core length was characterized by exit shape factor. In literature, the supersonic jet characterization and the related experimental correlation are available for optimum expansion conditions whereas for other expansion (under and over) conditions the experimental correlations are barely available. While investigating experimentally, a new empirical relation was obtained which was the improved form of earlier correlations for supersonic core length. The current results obtained from three different methods (total pressure data, schlieren image and numerical simulation) had shown the reasonable agreement with the experimentally obtained relation.