Abstract Transverse magnetoresistance in amorphous magnetic alloys (Fe1-xCox)82Cu0.4Si4.4B13.2 were measured at room temperature and in the magnetic field range 0-15 kOe. For large magnetic field, three various functional dependences of magnetoresistance on magnetic field strength have been found as follows: (1) △ρ/ρ approaches saturation. (2) △ρ/ρ increases proportionally to H2. (3) For x = 0.15, sharp △ρ/ρ peak appears at certain magnetic field strenght in spectial angular orientation of both magnetic and electric current. The case (3) is a magnetic breakdown phenomenon. Magnetic breakdown occurs at the gap between the spin-up and spin-down sheets of the Fermi surface. This gap is the spin-orbit gap and its magnitude is a sensitive function of magnetization. Hence the magnitude and wide of the magnetoresistance peak and the magnetic field strength at the peak point are functions of angular orientation of both magnetic field and electric current.