Iron oxides (group name) were precipitated by the hydrolysis of Fe(NO 3 ) 3 solutions in the presence of urotropin (hexamethylenetetramine). In an acidic medium at elevated temperature, urotropin undergoes hydrolysis with a gradual release of OH − ions. The precipitation time varied between 5h and 21days. The typical IR bands of the iron oxide phases were identified and used, together with XRD, to monitor phase changes in the precipitates. At the beginning of the precipitation process an amorphous phase was dominant and with prolonged time of Fe 3+ hydrolysis α-FeOOH was formed. α-FeOOH transformed to α-Fe 2 O 3 by the dissolution/reprecipitation mechanism. The concentration effect of urotropin on the phase composition of the precipitates after 7days of aging was observed with XRD, FT-IR and 57 Fe Mössbauer spectroscopies.