Unfamiliar second-language (L2) accents present a common challenge to speech understanding. However, the extent to which accurately recognized unfamiliar L2-accented speech imposes a greater cognitive load than native speech remains unclear. The current study used pupillometry to assess cognitive load for native English listeners during the perception of intelligible Mandarin Chinese-accented English and American-accented English. Results showed greater pupil response (indicating greater cognitive load) for the unfamiliar L2-accented speech. These findings indicate that the mismatches between unfamiliar L2-accented speech and native listeners' linguistic representations impose greater cognitive load even when recognition accuracy is at ceiling.