Macrobrachium straitus sp. nov. collected from Cochin Backwater along with M. idella and M. eguldens by cast net during August-November is described in detail. The species closely resembles M. equidens, but it could be immediately distinguished from latter by the longitudinal stripes along the entire body length. A comparative study on the zoeal stages of the two species reared in the laboratory showed morphological differences. Separate studies carried out on the breeding of these two forms indicated that no inter-breeding between them takes place. All these distinct differences necessitated to describe the striped form as a new species.