Abstract: Infra-red spectra of uranyl formate at room and low temperature (10K) are studied to probe the effect of temperature on peak width and peak position of the spectra. The vas of vibrational peak position of uranyl group O-U-O is determined accurately. The isotope shift of uranyl formate is estimated with different vas of 235U and 238U. The vibrational modes vas of 235U are 931.90 cm-m, 930.82 cm-1 and 930.74 cm-1 at 290 K,77 K and 10 K respectively. Isotope shifts Av(235U-238U)are about 0.63 cm-1,0. 67±0. 18 cm-1 and 0.71±0.21 cm-1 respectively, which approximate the values calculated theoretically.