Proteins from the loin tissues age ranged from 0 to 24 months of ten Korean cattle were extracted, separated and compared on two dimensional(2 D) gels to identify the proteins whose expression is highly correlated to marbling. We also compared the difference of loin proteins between castrated and non castrated bull cows on two dimensional gels. As the marbling in the loin of the cattle is optimized at 18 to 24 months, eight proteins expressed significantly higher level in 24 month than in 0 or 6 month were selected in terms of isoelectric points(pIs) and molecular weights. Using these values, we searched the Swiss Prot database via the ExPASy molecular biology server with TagIdent program. The proteins with the nearest molecular weights and isoelectric points were selected from the lists. These possible candidates were confirmed by N terminal microsequencing of the eight selected proteins. Three proteins, myoglobin, hemoglobin and ATPase, whose N termini were not blocked could be microsequenced and found to be exactly matched to the selected candidates. It is suggested that the proteins increasingly expressed in marbling periods can be involved in meat color, lipid transport and flavor improvement.