The　microstructure　evolution　and　mechanisms　of　globularization　of　TC21　titanium　alloy　with　lamellar　structure　were　investigated　during　hot　rolling　in　the　β　phase　and　α+β　phase.　The　results　show　that　the　prominent　effect　of　hot　working　parameters　on　the　break-up　and　globularization　of　TC21　titanium　alloy　with　lamellar　structure　is　found.　The　α　lamellar　structure　along　the　paralleling　rolling　orientation　and　adjacent　grain　boundaries　is　broken　up　and　globularized　and　the　intragranular　α　lamellar　is　buckled　and　kinked　when　TC21　titanium　alloy　is　processed　in　β　phase　region　(990°C)　at　strain　no　less　than　0.51　and　at　950°C　and　strain　0.92.　When　TC21　titanium　alloy　is　deformed　at　910°C　and　870°C,　α　lamellar　is　buckled　and　kinked　to　become　accordion.　Then,　by　TEM　analysis,　it　is　found　that　the　mechanism　of　globularization　of　TC21　titanium　alloy　with　α　lamellar　is　a　comprehensive　process　that　is　firstly　the　formation　of　α/α　interface　by　dynamic　recovery　or　boundary　splitting,　secondly　the　disintegrating　of　α　lamellar　due　to　diffusing,　and　finally　the　globularization　of　α　lamellar　by　termination　migration.