OBJECTIVE To analyze the constituent proteins in donkey hide, the key ingredient for Ejiao, an important traditional Chinese medicine for the blood-related conditions, in hope to eventually decipher the biochemical mechanism behind Ejiao's prominent medicinal efficacy. METHOD Two methods were employed to extract proteins in donkey skin. One used TriPure isolation reagent to extract the total proteins in donkey skin. Another used 1% sodium dodecyl sulfate (SDS) to heat the sample at 100 degrees C overnight. And then sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and capillary HPLC were used to analyze the component of proteins. RESULT There are not only collagen alpha1 (I) and collagen alpha2 (I), but also serum albumin in donkey skin. The content is over 25% in total proteins with the method of TriPure isolation reagent. The content of donkey serum albumin is up to 20% with the method of 1% SDS heating. And two bands, molecular weight are nearly 200 kDa,were found on 7.5% SDS-PAGE. Extracted these proteins to analyze with capillary HPLC, they were found to be the complex products of collagen and serum albumin of donkey. CONCLUSION Donkey serum albumin is a main protein component in the hide, which is a clue to expose is the effect of Ejiao on blood.