The thermal expansion of Fe-carbides Fe7C3 and Fe3C was measured above and below the ferromagnetic transition in a temperature range of 297-911 K by in situ X-ray diffraction enhanced by synchrotron radiation. The coefficient of thermal expansion was estimated as α = a0 + a1T. The results for paramagnetic phases are a0 = 3.1 × 10-5 K-1 and a1 = 1.2 × 10-8 K-2 for Fe7C3 and a0 = 3.9 × 10-5 K-1 and a1 = 1.2 × 10-8 K-2 for Fe3C. The ferromagnetic phases show linear relations with V298K = 371.9 Å3, a0 = 0.91 × 10-5 K-1 and a1 = 0 for Fe7C3 and V298K = 155.2 Å3, a = 0.86 × 10-5 K-1 and a1 = 0 for Fe3C. Our obtained results indicate that the coefficients of thermal expansion, that were calculated by high-pressure equations of state for Fe-carbides, appeared to be high-precision and consistent with the data obtained at 0.1 MPa.