The standard (p(o) = 0.1 MPa) molar enthalpies of formation of lanthanum(III), praseodymium(III), neodymium(III) samarium(III), gadolinium(III), dysprosium(III), holmium(III) and erbium(III) crystalline chelate complexes with 2,2,6,6-tetramethyl-3,5-heptanedione (dipivaloylmethane, HDPM) at the temperature 298.15 K were determined by precision solution and reaction calorimetry. From the available literature data of standard molar enthalpies of sublimation, the enthalpies of formation of the complexes in the gaseous state were obtained. The enthalpy changes of the dissociation reactions: Ln(DPM)(3)(g) = Ln(g) + 3 DPM. (g), Delta(diss)H(m)(o), were derived and the mean lanthanide-oxygen bond dissociation enthalpies, [D-m](Ln-O), calculated. The following values, were obtained: [GRAPHICS]