Q235　steel　is　widely　used　in　engineering　and　construction.　Therefore,　it　is　important　to　identify　the　damage　mechanism　and　the　acoustic　emission　(AE)　response　of　the　material　to　ensure　the　safety　of　structures.　In　this　study,　an　AE　monitor　system　and　an　in　situ　tensile　test　with　an　optical　microscope　were　used　to　investigate　the　AE　response　and　insight　into　the　damage　process　of　Q235　steel.　The　surface　of　the　specimen　was　polished　and　etched　before　the　test　in　order　to　improve　the　quality　of　micrographs.　Two　kinds　of　AE　responses,　namely　a　burst　and　a　continuous　signal,　were　recorded　by　the　AE　monitor　system　during　the　test.　Based　on　the　in　situ　test,　it　was　observed　that　the　damage　of　Q235　steel　was　induced　by　the　crystal　slip　and　the　inclusion　fracture.　Since　the　crystal　slip　was　an　ongoing　process,　continuous　AE　signals　were　produced,　while　burst　AE　signals　were　possibly　produced　by　the　inclusion　fracture　which　occurred　suddenly　with　released　higher　energy.　In　addition,　a　great　number　of　AE　signals　with　high　amplitude　were　observed　during　the　yielding　stage　and　then　the　number　and　amplitude　decreased.　©　2019　Polish　Academy　of　Sciences.　All　rights　reserved.