The dodecapeptide which is located in the hydrophilic loop connecting helix Ⅳ and Ⅴ of polypeptide D1 of spinach, was synthesized and convalently linked to BSA. Then the complex was injected into a rabbit. Nine weeks later, the specific antiserum was obtained, which showed high titer (1∶256) in immunodiffusion. Western blotting showed that there was an immunoaffinity reaction between the antibody and D1 band of PSⅡ reaction center D1-D2-Cyt b559 complex from spinach chloroplasts. Therefore, this antibody can be used as a probe to detect D1 protein and its degraded fragment during photoinhibition.