Formerly, the Hydro-treated Vegetable Oil (HVO) blended fuels has been studied by running the New European Driving Cycle (NEDC) and found that the higher HVO blended fuel can suppress NOX, lowering the particulate matter (PM) while improving the vehicle fuel economy. The result also shown that the 20% HVO + 5%FAME blended with diesel fuel has been proven to compatible with the advance diesel engine technology via the severe engine durability tests and fuel injection system tests. Therefore, the effects of two paraffinic diesel fuels, which are Gas-to-Liquid (GTL) and Hydro-treated Vegetable Oil (HVO), on a common-rail DI diesel engine have been mainly focused in this work. The main objective of this work was to study the relationships between fuel properties and theirs combustion characteristics by analyzing cylinder pressure data and exhaust emissions intensively. Subsequently, the research team needs to quantify the effectiveness of using GTL and HVO as a blending component for superior diesel fuel.The GTL and HVO were blended with a commercial grade B0 diesel fuel, into three candidate fuels such as 0%, 50% and 100%. All the blended fuels were tested on the engine dynamometer bench under the controlled condition at constant engine speed in two different injection modes (with and without pilot fuel injection). In both conditions, the GTL and HVO blended fuels show some improvement on diesel engine efficiency. Whilst increasing the GTL and HVO fractions, ignition delay for both pilot and main combustion events were decreased responsively, as well as the fraction of premixed combustion. Furthermore, the main combustion phase was also shifted due to the shorter combustion duration. According to the benefit on GTL and HVO fuels combustion characteristic, overall heat release rate curve was shifted and thermal efficiency was increased either. Regarding to the engine-out emissions, it has been found that GTL and HVO fractions help reducing all emission, with an exception for the Nitrogen Oxide (NOX). The reductions of Carbon Monoxide (CO), unburned hydrocarbon (THC) and Soot represent the improvement on combustion efficiency and brake fuel conversion efficiency. In summaries, GTL and HVO blended fuels show highly potential on becoming the fuel for advance common-rail DI diesel engine with the lower exhaust and energy consumption.