To provide a non-coat base fabric for air bags having low air permeability and a storage property without carrying out coating processing.

In the non-coat base fabric, a flat cross section fiber having a flat cross section in which a flatness ratio (a/b) obtained from long axial length (a) and short axial length (b) of a single yarn is 1.5-8 is used and a cover factor is 1,600-2,400 and a relationship between total fineness D1 (dtex) of warp and a yarn width W1 (mm) of a woven fabric and a relationship between total fineness D2 (dtex) of weft and yarn width W2 (mm) of the woven fabric each satisfy the following formulas: D1/W1=770-1,000 and D2/W2=770-1,000.