Effects of cultivars, cooking, and processing on hemagglutinin activity were evaluated by observing macroscopic hemagglutination using serial twofold dilution of trypsinized human blood type-O or rabbit blood. Hemagglutinin activity was expressed as maximal geometric dilution fold. Agglutination of rabbit blood was more sensitive compared to human blood. Hemagglutinin activities of glyphosate-tolerant soybean, HS2906, and imported conventional soybeans were not statistically different, although significant differences were observed among conventional soybean cultivars cultivated in Korea (286 to 1535 HU/mg protein). Time required to reach fifty percent inhibition of hemagglutinin activity ($IT_{50}$) value decreased with increasing cooking temperature and pressure. Most effective conventional cooking method to inhibit hemagglutinin activity was pressure-cooking ($IT_{50}$: 1.36 min). Calculated activation energy based on reaction rate constant was 4.88 kcal. No hemagglutinin activities were detected in processed soybean products such as tofu, soybean paste, and soysauce.