Abstract: The flame retardant viscose is obtained by adding silica to the viscose and subsequently fixing the silica to the fiber, such that the final flame retardant fiber will have regenerated cellulose and a silica polymer providing the fibers with flame retardant properties. Conventionally, the regeneration of the viscose mixture is carried out using zinc sulphate, while the final phase of washing of the fiber is accomplished using sulphuric acid. Both zinc and sulphuric acid are highly contaminating products from the environmental point of view. The invention consists, on the one hand, of replacing the zinc sulphate with aluminum sulphate and, on the other, of replacing the sulphuric acid with hydrogen peroxide or oxygenated water, this minimizing the contaminating effect of the process to an extraordinary extent.