PURPOSE: To provide the base suitable for production of photographic paper having high smoothness by decreasing the unequal thicknesses of a sheet-like base body to ≤1.00 μm in the integrated value (PY volue) of the power spectrum of the sheet-like base body surface.

CONSTITUTION: The base for the photographic paper having the good surface smoothness is effectively obtd. by using the sheet-like base body having the specific surface smoothness. The sheet base body having ≤1.0 μm, more preferably ≤0.80 μm integrated value (PY value) of the power spectrum at 1 to 12.5 mm wavelength is, thereupon, used. The measurement of the PY value is executed by using a film thickness gage, continuously measuring the unequal thicknesses of the sheet-like base body and subjecting the measured signal values obtd. in such a manner to a frequency analysis. Thus, the surface of the sheet-like base body has the excellent smoothness and is extremely useful for the production of the photographic printing paper having excellent smoothness.