The number and mass size distributions of refractory black carbon (rBC) cores in particles emitted from a diesel vehicle were investigated as a function of particle mobility diameter ( dmob) using a single particle soot photometer (SP2) and a differential mobility analyzer (DMA). The thickness and mass of coatings on the rBC cores were characterized. On the basis of the SP2 and DMA results, the physical properties of particles containing rBC, including effective density (ρeff), mass-mobility scaling exponent ( Dm), dynamic shape factor (χ), and mass absorption cross section (MAC), were derived as a function of dmob. At each dmob, the count median diameter (CMD) of the rBC cores was essentially the same as their mass median diameter (MMD), which increased linearly with dmob. The mass of the rBC cores was proportional to the cubic of their dmob. However, coating thickness on rBC cores remained unchanged with dmob, with an average thickness of 28.72 ± 4.81 nm. For particles containing rBC, ρeff decreased and χ increased with dmob. The Dm of particles containing rBC was calculated to be 2.09. At 355 and 532 nm wavelengths, the MAC of the diesel particles containing rBC was inversely dependent on dmob.