Abstract The beneficial combination of micro- and nano-patterned surfaces with magneto-optical materials was investigated over the recent years. Due to their resonant behavior, these structures are commonly used to enhance the non-reciprocal magneto-optical effects. In this paper, a novel kind of magneto-optical intensity effect is enhanced with an all-dielectric grating patterned on a magnetic nanocomposite layer. This nanocomposite is made of CoFe 2 O 4 nanoparticles (NPs) embedded in a silica matrix by sol–gel technique. The demonstrated magneto-optical intensity effect is reciprocal and it is observed with transverse magnetic field, for both polarization (TE and TM) and small angles of incidence. Such effect is not explained by the classical appearance of off-diagonal elements in the permittivity tensor of the magneto-optical material under magnetic field. However, it can be attributed to a magneto-induced reciprocal modification of the diagonal elements. Furthermore, this effect strongly depends on the NPs orientation inside the magneto-optical film and can originate from the magnetostrictive property of the magnetic CoFe 2 O 4 NPs.