Single crystal SmCo5 nanoparticles with an average size of 3.5 nm are produced by cluster-beam deposition. When deposited without matrix, the nanoparticles showed a super-paramagnetic behavior with a blocking temperature of 145 K. Dispersion of the SmCo5 nanoparticles in a carbon matrix results in an increase in both the coercivity and the blocking temperature. Room temperature coercivities as high as 12 kOe are obtained for the first time in mono-layers of SmCo5 nanoparticles dispersed in C matrix. δM plots show that the interactions in the samples are of exchange type, which can decrease the overall effective anisotropy and coercivity according to the random-anisotropy model. Coercivity is found to be inversely proportional to the packing density of the particles. SmCo5 nanoparticles with high coercivity are potential candidates for the next generation ultra high-density magnetic recording media.