Age　estimation　by　third　molar　mineralization　has　been　developed　for　a　period　of　time.　Recent　studies　showed　that　impaction　status　has　an　influence　on　the　rate　of　the　third　molar　mineralization　in　Europids　and　male　Black　African　populations.　In　this　regard,　the　present　study　was　conducted　to　determine　whether　the　impaction　status　could　delay　the　chronological　process　of　third　molar　mineralization　in　northwestern　Chinese　population　too.　A　total　of　3,512　digital　orthopantomograms　of　1,255　male　and　2,257　female　northwestern　Chinese　subjects　aged　from　11　to　26　years　were　assessed　based　on　the　formation　stages　described　by　Demirjian　et　al.　with　two　modifications.　Mineralization　stage　and　impaction　status　were　determined　for　all　third　molars.　Statistical　measures　were　calculated　at　stages　C-H　in　the　male　and　female　gender　for　both　impacted　and　non-impacted　third　molars.　It　was　ascertained　that　the　mean　ages　with　impacted　third　molars　at　stages　C-H　were　0.02-1.42　years　higher　in　males　and　0.04-1.52　years　higher　in　females　than　those　with　non-impacted　third　molars,　but　statistical　differences　were　only　found　at　stages　C,　D,　and　E　in　males　and　stages　D　and　E　in　females.　The　probabilities　of　being　under　14,　16,　or　18　years　of　age　with　non-impacted　third　molars　were　all　higher　than　those　with　impacted　third　molars.　The　results　prove　that　impacted　third　molars　show　significant　slower　mineralization　than　non-impacted　ones　at　stages　D　and　E　in　both　males　and　females　of　northwestern　Chinese　population.　It　is　recommended　to　consider　the　influence　of　impaction　on　the　rate　of　third　molar　mineralization　for　dental　age　estimation.