BS III norms (BS IV in 13+26 cities) have been implemented in India for a long time. There have been discussions over further country wide implementation of BS IV norms. All the engine categories (on-road & off-road) will be required to comply with stringent norms in future sooner or later.The Original Equipment Manufacturers (OEMs) have been working to comply with the norms. There has been a lot of work in the field of power train, transmission, aerodynamics etc. in order to make application better in all possible ways. However it has been largely focused on engine optimization and vehicle improvisation.The time has come when industry is staring on implementation of stringent emission norms and it will be vital to look at it in a whole perspective.It would not be incorrect to say there have been little work been done specifically on after-treatment systems which has been built for Indian market and driving conditions. Performance challenges with catalyst systems have been well known to OEMs as well system suppliers. This paper focuses one such effort which has been a gem to come out of the cooperation between OEM and system supplier.This work has been carried out to optimize the diesel oxidation catalyst for light commercial vehicle application for Indian market. During this project the size of the catalyst was reduced from 2 liters to around 0.3 liter while meeting the same (BS III) emission norms. This work underlines the necessity of after-treatment optimization in diesel engine focused on Indian market.