Here we present the result of measurements of electrical resistivity of ultra-disperse diamonds (UDD) with different graphitization degrees and onion-like carbon (OLC) prepared by vacuum annealing of UDD samples at various fixed temperatures. Intermediate samples contain particles with a diamond core covered by closed curved graphitic shells. The temperature dependence of electrical resistivity rho (T) of these structures is characteristic for the systems with localized electrons and variable hopping-length hopping conductivity (VHLHC). The data on sample resistance are discussed in terms of the variation of dimensionality of conductivity and changing the number of defects in the system.