The thermal expansion of the rare earth intermetallic compounds Sm3(CoxFe1-x)29-yCry (x = 0.9, y = 7; x = 0.8, y = 6.5; x = 0.7, y = 6) have been systematically investigated by high resolution synchrotron x-ray diffraction measurements (~120–480 K; ~ 300–823 K). The magnetic and thermal properties of Sm3(Fe0.9Co0.1)24Cr4 have been studied as a typical example of the Sm3(CoxFe1-x)29-yCry system by magnetic measurements (ac susceptibility, ~ 5–300 K; DC magnetisation, ~ 77–650 K) and specific heat measurements (~2–300 K). The Debye temperature of Sm3(Co0.9Fe0.1)22Cr7 was found to be θD = 410 ± 10 K from analyses of the specific heat data while the density of states at the Fermi level was N(EF) = 5.08 ± 0. 04 ev−1 atom−1. A pronounced contribution of the nuclear specific heat of Sm3(Co0.9Fe0.1)22Cr7 is evident below 5 K with the nuclear specific heat coefficient found to be A = 758 ± 30 mJ mol−1 K−1. Rietveld analyses of the x-ray diffraction data demonstrate the remarkable magneto-volume anomalies of Sm3(CoxFe1-x)29-yCry around their Curie temperatures TC with negative values of the volume magnetostriction detected below the Curie temperatures and values in the range ωs = − 1.1 × 10−3 to ωs = − 4.3 × 10−3 at 300 K.