The conformation effect on the infrared intensity of the characteristic bands (1230/1250 cm(-1)) of stereoregular isotactic poly(acrylonitrile) (PAN) was studied by the diffuse reflection (DR) and KBr disk methods. The DR spectroscopic features of isotactic PAN were briefly discussed. The intensity ratios (D-1230/D-1250) Of the IR bands in the original sample (A) and the dissolution-recovered sample (B) were compared: the intensity of the latter sample decreased more than that of the former, the extent of which was larger when the stereoregularity of the sample was higher. Little difference was observed in atactic PAN. These intensity variations were summarized as a function of the isotacticity of PAN, fr om which the effect of both conformation and configuration was quantitatively evaluated. The intensity difference between the DR and KBr disk re suits was also reasonably explained in terms of conformation. The IR behavior of other bands (1100 and 540 cm(-1) region) was briefly noted.