We report on a Mossbauer spectroscopic (MS) investigation of redox reactions of the vermiculite from Santa Olalla, Huelva, Spain. The spectrum of the sodium-saturated starting material can be interpreted by a superposition of three quadrupole doublets assigned to one Fe3+ and two Fe2+ C sites with octahedral coordination. The Fe2+ content determined by MS is about 10%. The isomer shift (IS; vs. the Co-57:Rh source) and the quadrupole splitting (QS) of the three iron sites vary in a small range of values depending on the form of the sample (crystals, powders) and the data analysis: IS of Fe3+ 0.26-0.27 mm/s, IS of Fe2+ 1.02 mm/s; QS of Fe3+ 1.02-1.04 mm/s, QS of Fe2+ 2.24-2.41 mm/s and 2.54-2.64 mm/s. Redox reactions have been carried out with H2O2, Na2S2O4, N2H4 and phenylenediamine. Fe2+ can be oxidized completely with H2O2, while the reduction of Fe3+ is much more difficult. Intercalating reducing agents (N2H4 and phenylenediamine) are acting most effectively. The maximum degree of reduction observed up to now was obtained with N2H4 and increased the amount of Fe2+ by a factor of three. The extent of reduction depends on pH, reaction time and/or the number of solution changes. The IS and QS values do not change significantly during the redox reactions except for the QS of the Fe3+ site which decreases with the degree of reduction to 0.89 mm/s.