Avian H7N9 influenza viruses cause sporadic outbreaks of human infections and threaten to cause a major pandemic. The breadth of B cell responses to natural infection and the dominant antigenic sites recognized during first exposure to H7 HA following infection are incompletely understood. Here, we studied the B cell response to H7 HA of two individuals who had recovered from natural H7N9 virus infection. We used competition-binding, hydrogen-deuterium mass spectrometry, and single-particle negative stain electron microscopy to identify the patterns of molecular recognition of the antibody responses to H7 hemagglutinin.