The present invention provides a high-strength galvanized steel sheet having excellent ductility, stretch flangeability, and fatigue resistance, and a method for manufacturing the same. A high-strength galvannealed steel sheet having excellent formability and fatigue resistance is characterized in that the steel sheet is composed of steel having a composition containing, by % by mass, C: 0.05% to 0.3%, Si: 0.5% to 2.5%, Mn: 1.0% to 3.5%, P: 0.003% to 0.100%, S: 0.02% or less, Al: 0.010% to 0.1%, and the balance including iron and unavoidable impurities, and the steel sheet has a microstructure containing 50% or more of ferrite, 5% to 35% of martensite, and 2% to 15% of pearlite in terms of an area ratio, the martensite having an average gain size of 3 μm or less and an average distance of 5 μm or less between adjacent martensite grains.