The purpose of the present invention is to provide a novel boron-containing compound utilizable in BNCT and so on and a process for preparing same. According to the process, a boron compounds having an amino acid skeleton containing cyclo-type rings or a pharmaceutically acceptable salt thereof is prepared, said boron compound being represented by general formula (I)[wherein l is an integer of 1 to 6; m is 0, 1, or 2; and n is 0, 1 or 2].