Abstract: Two experiments were conducted to test physical and chemical characteristics of organic Zn sources and their stabilities in vitro fermentation rumen. In experiment 1, physical and chemical characteristics of seven organic Zn sources were analyzed. The results showed that: Zn concentrations and amino acid composition of organic Zn sources varied greatly; Two organic Zn sources (ZnPro B and ZnAA B) had characteristic peaks of complexed Zn. The solubility of all Zn products was more than 90% in the buffer of HCl, citric acid and meutral ammonium citrate, and the solubility of Zn sources in pH2 buffer was ranged from 53.92% to 98.54%, and the solubility in water and pH5 buffer was changed from 6.04% to 98.54%; No complexed Zn was found for these organic Zn sources filtrates from pH2, 0.2 mol/L HCl-KCl, pH5, 0.1 mol/L KH₂PO₄- K₂HPO⁴ buffer, or deionized water; Four organic Zn sources showed weak complex strength, and one organic Zn source showed moderate complex strength, and two organic Zn sources showed strong complex strength. In experiment 2, a completely randomized design involving a 6×4 factorial arrangement of treatments was used to evaluate the stability of organic Zn sources with different complex strength in rumen by in vitro rumen fermentation method. The results showed that: The organic Zn sources with different complex strength were stable in the rumen in vitro, and the rumen by-pass ratio of them were more than 92%. The rumen by-pass ratio of organic Zn source with strong complex strength was the highest (99.55%), and that of organic Zn source with weak complex strength was in the middle (94.85%), and that of organic Zn source with moderate complex strength was the lowest (92.16%).