The radiopurity of a lithium molybdate (Li2MoO4) single crystal, a potential detector for the search for the neutrinoless double beta decay of 100 Mo, was studied deep underground at the Laboratori Nazionali del Gran Sasso (LNGS) (Italy). Data were collected with a crystal sample with a mass of 33.95g, using a high purity germanium (HPGe) detector with a total measurement time of 1240.3h. With the exception of slight pollution with 40 K ((170±80)mBq/kg), no other radioactive contaminants were found; the derived upper limits are: <20mBq/kg for 238 U chain, <30mBq/kg for 232 Th chain, <4mBq/kg for 137 Cs and <8mBq/kg for 60 Co.