Allergenicity of genetically-modified (GM) soybean was evaluated in male Sprague Dawley rats. To confirm the GM soybean used in this study, the polymerase chain reaction (PCR) was performed using the chromosomal DNA of soybeans. The PCR result provided the clear discrimination of genetically-modified (GM) soybeans. To evaluate the allergenicity of GM soybean and non-GM control one, the soybean homogenate was sensitized subcutaneously 3 times a week for 3 weeks. The doses of soybean were 0, 2 and 20 mg/kg in the protein basis. A week after the last sensitization, antisera were recovered from individual animals. When the sera were injected intradermally on the clipped back of unsensitized rats with various dilutions, followed by a challenge with 20 mg/kg of soybean homogenate containing 1% Evans blue, no sign of passive cutaneous anaphylaxis reaction was detected. In addition, when the sera were treated in the cultures of peritoneal mast cells, the increase of histamine release by anti-(GM soybean) sera was not observed when compared to that by anti-(non-GM soybean) sera. The present results indicate that the GM soybean might not act as a strong allergen in male Sprague Dawley rats.