Health　conditions　of　steel　strands　influence　directly　the　durability　and　security　of　whole　prestressed　structures.　Advanced　ultrasonic　guided　wave　technique　is　used　for　defect　detection　of　multi-wire　steel　stands　with　help　of　new　type　magnetostrictive　transducers.　A　kind　of　special　magnetostrictive　transducer　is　developed　for　the　excitation　and　reception　of　the　lowest　longitudinal　mode　L(0,1)　at　160kHz　which　is　suitable　for　defect　detection　of　steel　strands.　Artificial　notches　in　helical　and　central　wires　of　steel　strands　which　nominal　diameter　is　17.80mm　are　detected　using　L(0,1)　mode　excited　and　received　by　a　pair　of　magnetostrictive　transducers.　For　analyzing　the　sensitivity　to　the　notches　with　variable　depth　in　different　wires,　the　experimental　relation　curves　between　the　amplitudes　of　notch　echoes　and　the　notch　depths　are　obtained.　Experimental　results　show　that　ultrasonic　guided　waves　can　be　used　for　the　inspection　of　whole　steel　strands.　Furthermore,　from　the　amplitudes　of　defect　echoes　in　steel　strands,　it　is　obviously　found　that　L(0,1)　modes　is　much　more　sensitive　to　the　defects　in　helical　wires　than　ones　in　central　wires　although　the　sizes　of　these　defects　in　different　wires　are　almost　same.