Ac response of polycrystalline sodium yttrium fluoride (NaYF4) has been studied in the temperature region of 350-950 K and in the frequency range 50 Hz-100 kHz using blocking electrodes. From the admittance plots, the bulk conductivity (sigma), dielectric constant (epsilon’) and loss angle (tan delta) were determined at different temperatures and frequencies. The conductivity was found to increase with increasing temperature. Large value of epsilon’ observed at high temperatures was attributed to space charge polarization effects. The relaxation character of tan delta was observed. The ac conductivity was found to increase with increasing frequency.