Fibres of TiOSO4 . 2H(2)O are used as precursor material for the preparation of TiO2 fibres and/or particles with controlled morphology. This is achieved by heat treatment in air in the temperature range 580-1250 degrees C for times ranging from 0.1 to 100 h. Thermogravimetric studies showed that water was expelled at temperatures below 500 degrees C, and the conversion of TiOSO4 to TiO2 took place in the temperature range 540 to 580 degrees C. Heat treatment at temperatures below 650 degrees C yielded anatase, whereas rutile started to appear after extended holding times (100 h) at 650 degrees C. Heat treatment at 950 degrees C and higher yielded monophasic rutile samples. In the temperature region 650-950 degrees C, both anatase and rutile appeared in the product in various relative amounts depending on the temperature and time of annealing. The original fibre morphology was preserved in the low-temperature region where anatase was formed. In the rutile region, however, the fibres became degraded due to growth of TiO2 particles, resulting in pearl strings of particles. The final morphology of the product depended strongly on the time and temperature of heat treatment. The time dependence of the conversion of anatase to rutile at 750 degrees C was monitored. The rate of conversion is rather high in the beginning of the process but substantially slower at the end. The obtained data can be fitted by the extended rate law proposed by Prout-Tomkins.