A hydrogenation promoter of the present invention is produced by reacting
an alkyne compound or an alkene compound, a palladium compound
represented by a general formula Pd(II)X.sub.jL.sub.k (where L represents
a monodentate ligand or a polydendate ligand other than a
phosphorus-containing ligand (when two or more Ls are present in the
compound, the Ls may be the same or different), X represents an anionic
group, j represents a value determined according to the valence of X so
that X.sub.j has a valence of -2 as a whole, and k represents an integer
in the range of 0 to 4), and a base in an organic solvent. Specifically,
The hydrogenation promoter of the invention includes palladium
nanoparticles containing the alkyne compound or the alkene compound as an
agglomeration-preventing agent.