Two new m-oxalato-bridged CuⅡ2MⅢ-type (M=Cr and Fe) heterotrinuclear complexes have been prepared and identified as [Cu2Cr(ox)3(tmen)2]ClO4 (1) and [Cu2Fe(ox)3(tmen)2]ClO4 (2), where oxrepresents the oxalato dianions; tmen stands for N,N,N0,N0-tetramethylethylenediamine. The two complexes have not yet been isolated in crystalline form suitable for X-ray structure analysis, but based on elemental analyses, molar conductivity and magnetic moment (at room-temperature) measurements, IR, ESR and electronic spectra studies, it is proposed that these complexes have oxalato-bridged structure consisting of two copper(Ⅱ) ions and a chromium(Ⅲ) or an iron(Ⅲ) ion, in which the chromium(Ⅲ) or iron(Ⅲ) ion has an octahedral environment, and the two copper(Ⅱ) ions have a square-planar environment. The two heterotrinuclear complexes were further characterized by variable temperature magnetic susceptibility (4.2-300K) measurements and the magnetic data have been also used to deduce the indicated heterotrinuclear structure. The results derived from least-squares fit of the experimental data have confirmed that the adjacent copper(Ⅱ) and chromium(Ⅲ) ions through the oxalato-bridge in complex (1) are ferromagnetically coupled with the exchange integral J(Cu-Cr)=+10.2 cm-1, while an intramolecular antiferromagnetic coupling is detected between the copper(Ⅱ) and iron(Ⅲ) ions through the oxalato-bridge in complex (2) with the exchange integral J(Cu-Fe)=-11.6 cm-1, on the basis of the spin Hamiltonian operator, H =2J(SCu•SM+SCu2•SM) (M=Cr3+ or Fe3+).