Chromatic value b ^* in CIE colorimetric system of cotton fabric dyed with two typical stilbene type Fluorescent Brightening Agents (FBA) showed similar behavior to visual whiteness evaluated by white scale, so b ^* and visual whiteness reached maximum at the same FBA concentration on fabric. The fluorescence intensity at dominant wavelength (440 nm), however, did not agree with visual whiteness in the range of high concentrations. The effect of self-quenching or reabsorption on the change of fluorescence spectrum with FBA concentration showed as follows : (1) While the effect of self-quenching is small, reabsorption significantly influences on the fluorescence spectrum in the short wavelength region. (2) The contribution of reabsorption considerably changes at the region of FBA concentration where b ^* or visual whiteness reaches maximum. The concentration of FBA on fabric which leads to the maximum of visual whiteness, can be estimated from the relative changes of fluorescence intensities at two wavelength maxima (420, 440 nm) where reabsorption affected.