Encouraging the use of alternative fuels available in Thailand is mainly due to fuel crisis within the past few decades. The government has recently drafted a renewable energy long-term plan to increase biofuel production. This has emboldened biodiesel to be used as fuel for agriculture and transportation, in particular. Diesel engines are promising for reducing carbon dioxide emissions related fuel energy consumption. Ordinarily, diesel combustion generates particulate matter and nitrogen oxides in trade-off relationship. However, advanced techniques for engine technology and aftertreatment devices have been abundantly developed to mitigate these hindrances. To break the trade-off emissions, an example technique is to fuel engines with biodiesel incorporated with exhaust gas recirculation. Among available options, nonthermal plasma (NTP) is one of the techniques that charges exhaust gas with high power electricity to reduce some emissions. This paper investigates on a light-duty diesel engine running on biodiesel blends with steady-state controlled operational parameters. An NTP device is equipped to the exhaust system with load variation. Exhaust gas are measured prior to- and after- the NTP reactor in terms of smoke opacity and compositions, categorized by a thermo-gravimetric analysis. The NTP equipped engine can normally operate with lower gaseous emissions than those of non NTP equipped engine. This shows even more benefits when the engine is fuelled with biodiesel. It is suggested that used cars running on biodiesel blends can be modified with this technology in order to improve exhaust emissions to meet forthcoming tighten emission regulations as it does not require complex modification.