Cerium and bismuth have been successfully incorporated into (HoYb) 3-x-yCexBiyFe5O12 iron garnets with up to x=0.164 and y=0.665 by using the Bi2O3 self-flux growth technique. The (HoYb)2.171Ce0.164Bi 0.665Fe5O12 crystal has exhibited a much higher specific Faraday rotation of -1035 deg/cm and an equivalent absorption coefficient of 2.18 cm-1 at 1550 nm as compared with those of -588 deg/cm and 1.84 cm-1 for (HoYb)2.501Bi 0.499Fe5O12. The mixed effect of Ce 3+ and Bi3+ ions on the Faraday rotation has been analyzed qualitatively. In addition, due to the incorporation of Ce, the Faraday-rotation wavelength and temperature coefficients for (HoYb) 2.171Ce0.164Bi0.665Fe5O 12 are higher than those for (HoYb)2.501Bi 0.499Fe5O12 at 1550 nm. Despite this, (HoYb)3-x-yCexBiyFe5O12 has a great potential for application in 1550-nm optical isolators due to its large figure of merit of 109 deg/dB.