Discloses anti-N3pGlu A&bgr antibodies or antigen-binding fragments thereof and related compositions and therapeutic use of said compositions for treating Alzheimer&rsquos disease, Down&rsquos syndrome and cerebral amyloid angiopathy. The antibodies claimed comprise: LCDR1 of KS**SLLYSR*KTYLN, LCDR2 of AVSKL*S, LCDR3 of VQGTHYPFT and HCDR1 of GY*FT*YYIN, HCDR2 of WINPGSGNTKYNEKFKG, HCDR3 of EG*TVY.