The ultrasound-assisted freezing (UAF) process, the influence of UAF on the quality and microstructure of frozen dough, were investigated. Dough cylinders were immersion frozen in an ultrasonic bath with 25 kHz frequency and five different power levels. The results showed that UAF process was consists of three stages: a liquid-state temperature decrease stage, a phase-transition stage, and a solid-state temperature decrease stage; ultrasound enhanced heat transfer more efficiently in the latter two stages than in the first stage, due to more heat generation in the first stage. At 288 or 360W power levels, the total time for dough freezing shortened more than 11% significantly (P < 0.05), and the required time for each stage was reduced. Moreover, crystal nucleation was also enhanced by ultrasound with the formation of a large number of tiny ice crystals inside the frozen dough, and the maximum penetration force of ultrasound-assisted frozen dough increased. (C) 2012 Elsevier Ltd. All rights reserved.