Internet　of　Things　(IoT)　has　significantly　changed　our　lives　and　the　development　of　technology.　Different　types　of　smart　terminal　devices　are　connected　to　the　Internet　to　achieve　communications　with　each　other.　To　establish　the　connections,　communication　protocols　among　different　devices　should　be　unified.　Message　Queue　Teleme-try　Transport　(MQTT)　as　a　protocol　based　on　publisher/subscriber　and　broker　requires　a　small　amount　of　bandwidth　and　guarantees　the　message　passing　process　by　providing　different　Quality　of　Services　(QoS)　levels.　The　message　loss　for　the　subscriber　still　ex-ists　during　the　downtime　of　the　broker,　which　greatly　affects　service　qualities.　Currently,　the　message　loss　of　MQTT　is　mainly　collected　by　practical　experiments　which　costs　ex-tra　resources.　Therefore,　this　paper　proposed　a　statistical-based　message　loss　estimation　approach　to　analyze　the　message　loss　for　the　subscriber　when　MQTT　supports　different　QoS　levels.　The　proposed　method　can　estimate　the　message　loss　directly　from　the　derived　formula.　Numerical　analysis　is　adopted　to　prove　the　availability　of　the　message　loss　estimation　formulas.　©　2023,　Taiwan　Ubiquitous　Information　CO　LTD.　All　rights　reserved.