Doxycyline, prepd., e.g., by hydrogenation of 11a-chloro-6-deoxy-6-demethyl-6-methylene-5-hydroxytetracycline, was purified by heating the reaction mixt. with concd. HCl, pptn. with 5-sulfosalicylic acid, neutralization, salt formation with HCl, then pptn. as the complex with PhCH2NHCH2CH2NHCH2Ph and Ca ion.