Nanoparticles have recently been used as fuel additives to enhance diesel engine performance and exhaust gas emissions. Amino-functionalized multiwalled carbon nannotubes (NH2-MWCNTs) are catalysts that can be applied in diesel engines because of their promising properties. This study conducted an experimental investigation to determine the impacts of adding NH2-MWCNTs to diesel fuel using a single-cylinder CI engine running at a constant speed (1500 rpm) and various loads. The NH2-MWCNTs were added to diesel fuel at four concentrations of 25, 50, 75, and 100 ppm. Also, the same doses of pristine multiwalled carbon nanotubes (MWCNTs) were added to diesel to be used as a reference for NH2-MWCNTs. Most NH2-MWCNTs blends were preferred in combustion characteristics, engine performance, and exhaust emissions compared to diesel and MWCNTs blends. Thus, there was a considerable increase in cylinder pressure and heat release rate compared to pure diesel. Also, the brake thermal efficiency was increased, and the brake-specific fuel consumption was decreased compared to diesel. Most NH2-MWCNTs combinations appeared to decrease NOx, soot, and CO levels significantly. The NH2-MWCNTs blends are generally favored over the pristine MWCNTs blends in reducing exhaust emissions.