Long　cortical　bone　allows　axial　transmission　of　ultrasonic　guided　waves,　which　has　been　utilized　for　osteoporosis　evaluation.　Benefiting　structural　and　molecular　sensitivity,　photoacoustic　has　been　used　for　tissue　composition　characterization.　However,　photoacoustic　guided　waves　(PAGWs)　in　long　cortical　bone　as　well　as　the　influence　of　optical　transmissivity　on　PAGWs　have　not　been　thoroughly　investigated.　In　the　study,　the　influence　of　optical　transmissivity　on　the　signal　characteristics　of　PAGWs　was　experimentally　studied　with　a　1064　nm　pulsed　laser　ultrasonic　system　and　a　tunable　laser　system　(wavelength　range:　650-2600　nm).　Results　show　that　dispersion　curves　of　PAGWs　are　not　significantly　affected　by　the　optical　transmissivity;　while　photoacoustic　guided　modes　and　signal　spectrum　are　sensitive　to　the　optical　transmissivity　in　cortical　bone.　In　experiments,　the　lasers　with　high　transmissivity　can　emit　pure　A0　mode　PAGWs　at　the　low　frequency,　around　22　kHz,　in　the　relatively　thick　6.2　mm　bone　plate;　on　the　contrary,　both　A0　and　S0　modes　are　generated.　The　slope　of　power　spectrum　density　(PSD)　of　PAGWs　decreases　with　the　increase　of　transmissivity,　and　the　decline　rate　is　around　-0.229.　The　study　proves　the　correlation　between　the　signal　characteristics　of　PAGWs　and　the　optical　transmissivity,　it　is　helpful　for　the　development　of　PAGWs　in　long　cortical　bone　towards　the　osteoporosis　evaluation.