Abstract Some cobalt(III) complexes with Co–C σ-bond have been prepared by photodecarboxylation reactions of the complexes containing ethylenediamine-N,N′-dipropionate (eddp) or its analogs. The crystal structure of α-[Co(Me2eedmp-C,N,N′,O)(en)]+ (Me2eedmp: −CH2CH2N(CH3)(CH2)2N(CH3)(CH2)2COO−), which is the photolysis product of α-[Co(Me2eddp)(en)]+ (Me2eddp: {CH2N(CH3)(CH2)2COO−}2), was determined by the X-ray diffraction method. The crystal is monoclinic, space group P21/n, a = 9.013(2), b = 13.420(1), c = 14.754(4) Å, β = 92.75(1)°, V = 1782.5(6) Å3, Z = 4, and R = 0.038. The coordination of C atom to Co center results in elongation of the Co–O bond located in the trans position of the C atom, compared with usual Co–O bonds. The photolysis products of optically active isomers (Λ-α, Λ-β(1), and Λ-β(2)) of [Co(eddp)(en)]+ were studied on the basis of the absorption, CD, and 13C NMR spectral data. The photolysis of Λ-β(1) provided Δ-α-[Co(eedmp-C,N,N′,O)(en)]+ (eedmp; −CH2CH2NH(CH2)2NH(CH2)2COO−), while the photolysis of Λ-β(2), which is a conformational diastereomer of Λ-β(1), provided (−)CD543-β-[Co(eedmp-C,N,N′,O)(en)]+ (major product) and Λ-α-[Co(eedmp-C,N,N′,O)(en)]+. Optically active (+)CD553-β-[Co(etnmp-C,N,N′,O)(en)]+ (etnmp: −CH2CH2NH(CH2)3NH(CH2)2COO−) was obtained by the photolysis of Δ-(−)CD505-β-[Co(tndp)(en)]+ (tndp: CH2{CH2NH(CH2)2COO−}2).