Nanodiamonds (NDs) were synthesized under atmospheric conditions by heating a precursor powder mixture consisting of naphthalene and a microwave (MW) absorbing material inside an ordinary MW oven for 10 min. Pyrolysis of naphthalene led to the formation of onion-like carbon particles which then converted to NDs after prolonged MW irradiation. Different carbon-based materials like graphite, carbon black, graphene, and carbon nanotubes were used as microwave radiation absorbers that assisted in the dissociation of naphthalene and formation of NDs. ND particles were formed in both isolated as well as aggregated forms. Size of the particles ranged from 2 to 700 nm. Scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy, Raman spectroscopy and thermogravimetric analysis were used to characterize the NDs present in the MW-synthesized product. The proposed MW-based ND synthesis technique is simple, fast, inexpensive, energy efficient and could be suitable for industrial scale production.