1,3-Dienolate dipalladium(I) complex [{μ-CH 2 C(O)CH CH 2 }Pd 2 (PPh 3 ) 2 (μ-Cl)] (2) is prepared and characterized. Complex 2 is easily protonated to yield 2-hydroxy-1,3-butadiene dipalladium(I) complex [{(μ-η 2 :η 2 -CH 2 C(OH)CH CH 2 }Pd 2 (PPh 3 ) 2 (μ-Cl)][BF 4 ] (3). On the basis of the comparative analyses on IR and NMR spectra and X-ray structure analysis, the co-ordination mode of 1,3-dienolate on Pd Pd is revealed to involve the resonance between C-bound and π-olefin-bound enolate structures.