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• Heat capacity and cell parameters of TmB 2 C at 2–300 K are experimentally studied. • The impact of crystal field on TmB 2 C heat capacity has been revealed. • Thermal expansion of TmB 2 C in the basal plane is almost missing. • Anomalies in thermal expansion are due to magnetic phase transition and CEF impact. Temperature dependences of heat capacity C P (T) and lattice parameters a(T) , b(T), c(T) of thulium carboboride TmB 2 C at 2–300 K were experimentally studied. Magnetic phase transition in the carboboride – 'paramagnetic – antiferromagnetic' at T N = 11.0 K was revealed. By comparison with the diamagnetic LuB 2 C the Schottky contribution to TmB 2 C heat capacity due to the crystal electric field (CEF) was calculated. The splitting scheme of Tm3+ ion f – level by the crystal field was suggested. It was obtained that in the temperature range under study (5–300 K) TmB 2 C carboboride thermal expansion in the basal plane is almost missing (anisotropic invar effect, linear thermal expansion coefficient α a (T) ≃ α b (T) ≃ 0). It is, seems, a common property of the lattice dynamics of layered carboborides. The anomalies in the thulium carboboride thermal expansion are due to the magnetic phase transition and the CEF influence. [ABSTRACT FROM AUTHOR]