The present application relates to compositions of humanized and humanized/deimmunized anti-endoglin antibodies and antigen-binding fragments thereof. One aspect relates to antibodies having one or more modifications in at least one amino acid residue of at least one of the framework regions of the variable heavy chain, the variable light chain or both. Another aspect relates to antibodies which bind endoglin and inhibit angiogenesis. Another aspect relates to the deimmunization of humanized antibodies to reduce immunogenicity. Another aspect relates to the use of humanized and humanized/deimmunized antibodies which bind endoglin for the detection, diagnosis or treatment of a disease or condition associated with endoglin, angiogenesis or a combination thereof.