Significance A recent outbreak of chikungunya virus in the Americas has caused more than one million infections in humans. The reemergence of this virus has become a major threat to public health due to a lack of available vaccines and antiviral drugs. We determined the cryo-EM structures of chikungunya virus particles complexed with two of the most potent human antibody fragments described in a previous study. Both antibodies neutralized the virus by stabilizing the position of the viral surface glycoproteins, which blocks the exposure of the glycoprotein fusion loops required to initiate viral entry into the cytoplasm of a target cell.