Ultrafine titania particles were synthesized by hydrolysis of titanium tetraisoproxide (TTIP) in the nanodroplets of water/NP-5/cyclohexane microemulsions. The as-prepared particles were amorphous, transformed into the anatase phase at 450 degreesC, and completely into the rutile phase at 700 degreesC. The amorphous-to-anatase phase transition temperature decreased with increasing water/surfactant molar ratio. With increasing temperature from 500 to 900 degreesC, the crystallite size increased about twice from 11.7 to 24.4 nm, while the size of the secondary particles, agglomerates of the primary particles, increased by a factor of about 10. The particles grew largely by intra-agglomerate densification below 700 degreesC, whereas they grew by interagglomerate densification above 700 degreesC. The anatase phase formed at 500-600 degreesC showed considerable photoactivity for the degradation of phenol, whereas both the amorphous phase at 300 degreesC and the rutile phase at 700 degreesC were almost inactive for this reaction.