(3‐Mercaptopropyl)trimethoxysilane (MPTMS)‐ethanol‐solution‐treated nitrile butadiene rubber/nanodiamond (NBR/ND) polymer‐matrix nanocomposites were prefabricated in situ using a facile environmentally friendly one‐pot design. The MPTMS‐modified ND (MND) and pristine ND were characterized using wide‐angle X‐ray diffraction, Fourier‐transform infrared spectroscopy, transmission electron microscopy, N2 adsorption analysis, thermal gravimetric analysis, and X‐ray photoelectron spectroscopy. The pristine ND exhibited a high specific surface area and abundant active organic groups, especially hydroxyl and carboxyl groups, thus confirming its hydrophilic properties. The successful fabrication of surface‐modified MND was also verified. The fracture surface morphologies of the NBR/MND nanocomposites were analyzed using high‐resolution scanning electron microscopy and field‐emission transmission electron microscopy, and the dynamic rheological properties of the NBR/MND nanocomposites were characterized using a rubber processing analyzer. The NBR/MND composites exhibited superior mechanical properties, which were attributed to the strong interfacial interaction of the MND particles with the NBR matrix via MPTMS linking. POLYM. COMPOS., 39:3472–3481, 2018. © 2017 Society of Plastics Engineers