The　assessment　of　bio-cementation　effect　using　nondestructive　testing　methods　is　important　for　the　application　of　microbial-induced　carbonate　precipitation　(MICP)　technique.　In　this　study,　a　special　grouting　system　was　designed　to　conduct　the　bio-grouting　of　shale　soils　on　a　testing　model.　The　ultrasound　technique　was　used　to　evaluate　the　effectiveness　of　bio-cementation.　A　method　was　derived　to　esti-mate　the　distribution　of　ultrasonic　wave　velocity　values　within　the　testing　model　based　on　the　average　values　measured　on　the　model　surfaces.　From　the　changes　of　isosurfaces　of　velocity　values,　the　evolution　of　soil　improvement　within　the　model　corresponding　to　the　different　number　of　grouting　cycles　was　analyzed　numerically　and　visually.　The　SEM　imaging　technique　was　used　to　illustrate　the　mechanism　of　influence　of　the　calcium　carbonate　precipitation　on　the　wave　velocity　of　the　bio-cemented　specimen.　The　linear　relation-ships　were　established　among　the　ultrasonic　wave　velocity,　unconfined　compressive　strength　(UCS),　and　the　amount　of　CaCO3　precip-itations　formed　in　the　MICP　process.　In　combination　with　the　application　of　the　ultrasound　measurement　technique　as　demonstrated　in　this　work,　the　relationship　provides　a　very　useful　nondestructive　testing　tool　to　assess　the　effectiveness　of　bio-cementation　within　a　large　soil　body.&　COPY;　2023　Production　and　hosting　by　Elsevier　B.V.　on　behalf　of　The　Japanese　Geotechnical　Society.　This　is　an　open　access　article　under　the　CC　BY-NC-ND　license　(http://creativecommons.org/licenses/by-nc-nd/4.0/).