Due　to　the　premium　flavor,　Qingxin　oolong　tea　(QOT),　which　is　grown　and　produced　in　Taiwan,　is　widely　appreciated.　Roasting　is　a　crucial　process　for　shaping　its　flavor.　However,　the　effect　of　roasting　on　the　aroma　and　taste　of　QOT　was　not　fully　understood.　In　this　study,　the　volatile　composition,　aroma-active　compounds　and　phenolic　profile　of　QOT　with　different　roasting　degrees,　including　the　unroasted　(UR),　the　medium　roasted　(MR)　and　the　heavy　roasted　(HR)　were　analyzed.　As　revealed　by　headspace　solid　phase　microextraction　gas　chromatography-mass　spectrometry　(HS-SPME-GC-MS)　and　multivariate　statistical　analyses,　UR　and　MR　demonstrated　similar　volatile　profiles,　while　heavy　roasting　changed　the　volatile　composition　greatly.　Multiple　nitrogen-containing　compounds,　such　as　3,5-diethyl-2-methylpyrazine　and　2-ethyl-3,5-dimethylpyrazine,　were　uniquely　found　in　heavy　roasted　samples,　which　can　be　ascribed　to　the　extensive　Maillard　reaction.　Moreover,　eight　compounds　were　identified　and　verified　as　key　aroma-active　compounds　by　using　gas　chromatography-olfactometry-mass　spectrometry　(GC-O-MS),　aroma　recombination　and　omission　experiments.　The　aldehydes　and　alcohols,　such　as　linalool,　benzeneacetaldehyde　and　alpha-farnesene,　with　a　floral　scent　were　the　dominant　aroma-active　compounds　in　UR　and　MR,　while　2-ethyl-3,5-dimethylpyrazine　and　3,5-diethyl-2-methylpyrazine　with　a　roasted　scent　were　the　main　aroma-active　compounds　in　HR.　Furthermore,　as　revealed　by　ultra-high　performance　liquid　chromatography　and　Orbitrap　high　resolution　mass　spectrometry　(UHPLC-Q-Orbitrap-MS),　flavanols　and　phenolic　acids　were　significantly　lower　in　abundance　in　UR　and　MR　as　compared　to　those　in　HR,　whereas　flavonols　were　less　affected　by　roasting.　These　findings　provide　useful　information　for　understanding　the　flavor　characteristics　of　this　popular　oolong　tea　for　the　first　time.