Skin will undergo changes in biochemical and biophysical properties during leather processing.rnBiochemical composition varies with respect to different regions of the skin like butt, belly,rnand neck. Supported with the nature of structure and chemical constituents of the skin, leatherrnprocessing chemicals do have different propensity to different parts of the skin. Belly regionâ€™srnlooseness and substance non-uniformity are the main problem in leather making from sheeprnskin (SS) particularly for shoe upper. Having a back with the leather processing practice andrnstatistical data, an exuberant substance non-uniformity for sheep shoe upper is still recurrent inrnour countryâ€™s context. To address same issue, this work focusses on the analysis of histologyrnand biochemical properties of butt and belly portion of hair sheep skin besides the investigationrnof application collagen hydrolysate on the value addition of dyed crust leather and emissionrnload during pre-tanning.rnGlobular proteins are relatively higher in the butt region than the belly, whereas it is reverse inrnthe case of fibrous proteins except collagen. Interestingly, the presence of proteoglycansrncontent in butt regions is significantly high compared to belly and in case of fat it is reverse.rnThus, the effect of liming and bating operations in removing unwanted skin constituents isrnstronger in butt and belly regions of SS, respectively, which reflects the requisite importancernof the two unit operations in the pre-tanning operations. ASC contribution is higher in buttrnregion than belly and the reverse is true in the case of PSC. The overall collagen content isrnconsiderably higher in butt than belly which may be the major cause of the higher strengthrncharacteristics of butt regions. Cr2O3 content is high in butt region than belly whichrncorroborates with protein content and its interaction with tanning agents. Distribution of porernsize influences the breathability property of leather which has been seen to vary in all the unitrnoperations. Scanning electron microscope study complements same trend with respect tornchanges in the cross-section of the skin during leather processing. Therefore, the considerablernvariations observed among the two regions of SS would help the tanners and chemicalrnmanufactures to have more information on the parts of skins so as to improve the cutting valuernof the thin part of skin.rnCollagen hydrolysate being prepared under thermal alkaline condition enhances the hidernsubstance of both belly and butt regions of sheep skin during pre-tanning when offered at pHrn9.0. Despite the fact that Cr2O3 uptake found to be reduced in same way the CH uptakernincreased in both regions of SS, the Ts still found to be greater than 90oC thereby strengtheningrnxvrnthe application of CH in leather processing. In addition to the pore size distribution of thernregions of SS, it has been observed that the fibre density of skin matrix also plays its own partrnfor the uptake and retainment of treatment chemicals. The higher increase in the protein contentrnof butt part of SS than belly augments same. The dyestuff exhaustion is by far better for CHrntreated leather than commercial protein fillers (CPF) used during the study. The increased inrnthe dye exhaustion and overall physico-chemical properties of CH treated upper leathers wouldrnhighly help the competitiveness of the tanner for the use of CH particularly coined as wealthrnfrom waste. The use of CH would be convenient for the value addition of lower end products.rnThe emission load of tanning process liquor with CH is higher than conventional one and samernis true for post-tanning process liquor with CPF.