The semi-metallic cubic compound YBiPt doped by Er 3+ (4f 11 ) has been studied by ESR technique between 4 and 300 K. X-band and Q-band measurements have been performed. The angular dependence of the ESR spectra on the crystal orientation with respect to the static magnetic field has been measured. Two anisotropic lines with hyperfine peaks coming from the interaction between electronic and nuclear spins of 167 Er 3+ (I = 7/2) isotopes have been observed below 30 K in the spectra. Computer modeling showed that these lines are the ESR signals from the quadruplet ground state of Er 3+ ions in the cubic crystal field. The values of crystal field parameters B 4 = -5.68 × 10 -4 cm -1 and B 6 = -6.64 × 10 -6 cm -1 have been extracted. Also an isotropic line near g = 2 have been observed in both frequency bands. Dysonian lineshape of the spectra components due to the skin-depth effect shows the conducting property of the sample under study. The temperature dependence of the spectra intensity obeys the well-known Curie law for paramagnetism arising from the unpaired electrons of Er 3+ ion.