The　incidence　of　scarlet　fever　and　pertussis　has　increased　significantly　in　China　in　recent　years.　During　the　COVID-19　pandemic,　stringent　non-pharmaceutical　intervention　measures　were　widely　adopted　to　contain　the　spread　of　the　virus,　which　may　also　have　essential　collateral　impacts　on　other　infectious　diseases,　such　as　scarlet　fever　and　pertussis.　We　compared　the　incidence　data　of　scarlet　fever　and　pertussis　in　Mainland　China　and　Hong　Kong　from　2004　to　2021　before　and　after　the　COVID-19　pandemic.　The　results　show　that　the　incidence　of　both　diseases　decreased　significantly　in　2020-2021　compared　to　the　after-re-emergence　stage　in　these　two　locations.　Specifically,　in　2020,　scarlet　fever　decreased　by　73.13%　and　pertussis　by　76.63%　in　Mainland　China,　and　83.70%　and　76.10%,　respectively,　in　Hong　Kong.　In　the　absence　of　COVID-19,　the　predicted　incidence　of　both　diseases　was　much　higher　than　the　actual　incidence　in　Mainland　China　and　Hong　Kong　in　2020-2021.　This　study　demonstrates　that　non-pharmaceutical　measures　implemented　during　the　COVID-19　pandemic　can　partially　reduce　scarlet　fever　and　pertussis　re-emergence　in　Mainland　China　and　Hong　Kong.