Three grades of vapor grown carbon nanofibers (pyrolytically stripped, heat-treated, heat-treated and oxidatively treated) with diameters 100-350 nm were tested for their tensile strength and interface adhesion properties by a novel MEMS-based mechanical testing platform. The nominal tensile strengths of the pyrolytically stripped and the heat-treated nanofibers followed Weibull distributions with characteristic strengths between 2.8-3.4 GPa. The true material strengths, excluding the hollow fiber cores, were ∼33% higher than the nominal strengths. The nanofiber fracture surfaces indicated brittle fracture and slip of the oblique graphene layers of the nanofiber backbone. SEM and TEM images of matching ends at the rupture sites pointed to a failure geometry that agrees with the stacked truncated cone structure of vapor grown carbon nanofibers. Furthermore, pull-out experiments of individual vapor grown carbon nanofibers provided their average interfacial shear strength (IFSS) in EPON epoxy matrices. The IFSS for the non-surface-functionalized, high-temperature-heat-treated nanofiber-epoxy system averaged ∼55 MPa, revealing that the adhesion and bonding of the heat-treated, non-functionalized carbon nanofibers is quite better than that of non-functionalized carbon fibers (15-28 MPa) and as good as that of functionalized carbon fibers (40-65 MPa).