Experimental　investigations　on　the　characteristics　of　air-water　two-phase　flow　in　the　vertical　helical　rectangular　channel　are　performed　using　the　high　speed　flow　visualization.　The　flow　pattern　map　and　the　transition　in　the　helical　rectangular　channel　are　presented.　The　flow　pattern　evolution　in　different　positions　of　the　helical　rectangular　channel　is　illustrated.　The　discussion　on　the　coalescence　of　the　bubble　and　slug　is　presented.　The　slug　velocity,　slug　length　distribution,　liquid　slug　frequency,　falling　liquid　film　velocity　and　falling　film　thickness　along　the　slug　are　investigated.　The　dimensionless　liquid　film　thickness　of　the　annular　flow　on　the　outer　side　of　the　channel　is　measured　using　the　digital　image　processing　algorithm.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.