The magnetic chemically peculiar star nu Fornacis is known to be a periodic magnetic and luminosity variable. In the framework of the Oblique Rotator Model, nu For presents a mainly dipolar magnetic field, whose symmetry axis is tilted with respect to the rotational axis, non solar abundances and a non homogeneous distribution of elements on the stellar surface. The variability period is the stellar rotational period. Thus, spectral variabilities are also expected for this star. By analysing the Hipparcos photometry and data from the literature, the luminosity period of nu For has been found equal to 1.89232 days. This value also represents the variability of the effective magnetic field measurements available in the literature. To investigate the, up to now unknown, spectroscopic behaviour of nu For, we have performed time-resolved spectroscopy of this star in the 400-600 nm range. The equivalent widths are found to be also variable with the previous period and have been used to derive abundances. Phase relations, between light, spectral and magnetic variabilities have been established. According to the hypothesis that light variations are due to a non-homogeneous distribution of elements on the stellar surface and high metallicity regions are responsible for blocking of ultraviolet flux and its redistribution towards the visible wavelengths, iron is the main origin of the light variability.