The applicability of Ce and Y as promising candidate elements to form irreversible traps in weld metal was investigated by thermal desorption spectroscopy(TDS) with gas chromatography(GC). The precise nature of the precipitate particles newly formed in the weld metal by the addition of Ce and Y to a certain alloy system was characterized. Moreover,the hydrogen trapping efficiency expressed as the reduction of the diffusible hydrogen in the weld metal was analyzed. The results showed that the addition of Ce and/or Y to this alloy system led to the formation of a mixed type of(Ce,Ti)-based oxide,(Y,Ni)-based carbide,or(Ce,Y,Ti)-based oxide particles. Because of the high activation energy of the mixed type of particles(≥ 150 k J/mol),the trapping efficiency for hydrogen was considered to be sufficiently high to effectively reduce the diffusible hydrogen content. The applicability of Ce and Y as promising candidate elements to form irreversible traps in weld metal was investigated by thermal desorption spectroscopy (TDS) with gas chromatography (GC). The precise nature of the precipitate particles newly formed in the weld metal by the addition of Ce and Y to a certain alloy system was characterized. Moreover, the hydrogen trapping efficiency expressed as the reduction of the diffusible hydrogen in the weld metal was analyzed. The results showed that the addition of Ce and / or Y to this alloy system led to (Ce, Ti) -based oxide, (Y, Ni) -based carbide, or (Ce, Y, Ti) -based oxide particles. Because of the high activation energy of the mixed type of particles (≥ 150 k J / mol), the trapping efficiency for hydrogen was considered to be sufficiently high to effectively reduce the diffusible hydrogen content.