The thermodynamic properties of ErSi and ErSi 1.67 are investigated for the first time within the temperature range of 52-300 K. Enthalpy (J ⋅ mole −1 ), heat capacity, entropy, and Gibbs free energy (J ⋅ mole −1 ⋅ K −1 ) at 298.15 K are calculated: Cº p (T) = 47.08 ± 0.19; Hº(T) − Hº(0 K) = 9701 ± 49; Sº(T) = 70.5 ± 0.6; Φº(Τ) = 38.0 ± 0.6 (ErSi); Cº p (T) = 60.65 ± 0.25; Hº(T) − Hº(0 K) = 12710 ± 64; Sº(T) = 93.5 ± 0.8; Φº(T) = 50.9 ± 0.8 (ErSi 1.67 ).