BackgroundWhile　restriction　measures　are　critical　in　containing　the　COVID-19　outbreak,　limited　studies　have　investigated　the　behavioral　and　psychological　impact　of　these　measures.　This　study　aimed　to　investigate　the　effects　of　physical　and　sedentary　behavioral　changes　and　online　behavior　during　the　COVID-19　pandemic　on　mental　health　and　life　satisfaction　among　the　Chinese　population.　MethodsThe　data　were　obtained　from　a　cross-sectional　survey　of　2145　residents　aged　between　18　and　80　in　Hubei　province,　China　between　March　23,　2020,　and　April　9,　2020.　ResultsParticipants　who　had　high　frequencies　of　physical　activities　before　or　during　the　COVID-19　outbreak　exhibited　higher　levels　of　life　satisfaction.　Participants　who　increased　their　sitting　time　during　the　pandemic　or　kept　sitting　for　more　than　eight　hours　before　and　during　the　pandemic　reported　worse　mental　health　than　those　who　maintained　less　sedentary　behavior.　Besides,　participants　who　used　the　Internet　for　information　seeking,　communication,　and　entertainment　more　frequently　reported　better　mental　health　and　life　satisfaction.　In　contrast,　there　was　a　positive　association　between　commercial　use　of　the　Internet　and　symptoms　of　mental　disorders.　ConclusionGiven　the　link　between　physical　and　sedentary　behavioral　changes　with　worse　mental　wellbeing,　strategies　to　reduce　sedentariness　and　increase　physical　activity　during　the　COVID-19　pandemic　are　needed.