To obtain high strength steel sheet with high press formability and excellent galvannealing properties, molybdenum and carbon were chosen as strengthening alloy element. Molybdenum gave strengthening about 6MPa/0.1%, and carbon gave about 8.5MPa/10ppm. In both case, deterioration in formability was small. Steel containing molybdenum and carbon exhibited highest formability in case coiling at about 600°C. Applying these results and containing 100ppm carbon and 0.2% molybdenum, high strength galvannealed sheet steel of 440MPa grade with elongation of 35% and r value of 1.5, was developed. This steel also exhibited good galvannealing properties.