This work presents the effect of the Di-tetra-butyl-peroxide (DTBP) as an oxygenated additive on neat used mustard oil biodiesel (B100) to evaluate the emission and performance engine characteristics. Four fuels, namely, diesel, biodiesel (Mustard biodiesel), a blend of B100-10percentage, and 20% by volume of DTBP (BD90DTBP10 and BD80DTBP20) are prepared and tested on a single cylinder, constant speed diesel engine. Experimental outcomes revealed that 20% of DTBP reduces 7.3% CO, 5.1% HC, and 4.6% NOx and 3.2% smoke emissions of B100. From this study, further, it is inferred that BD80DTBP20 blend could be utilized as an alternative fuel for a CI engine with no modifications in engine design.