The quantitative analysis of precipitates in ferrite was investigated using the fact that the formation of precipitates in Nb, V and Ti added steels accelerated austenite/ferrite transformation. The major factors on austenite/ferrite transformation were cooling rate, austenite grain size, and deformation. The slower cooling rate, the smaller austenite grain size and the higher deformation accelerated austenite/ferrite transformation. In 0.34wt%V micro-alloyed steel, the influence of cooling rate and austenite grain size on austenite/ferrite transformation was investigated without deformation. In addition, the experimental method was set up to measure the amount of precipitates in ferrite by the transformation dilatometer. The amount of precipitates was controlled by the holding temperature and time in ferrite. Then, the specimen was inversely transformed without the formation or dissolution of precipitates. Volume fractions transformed were measured by dilatometer during cooling. Iso-precipitation kinetics was determined by comparing the mean transformation temperatures at various conditions, respectively. The result was compared with the calculated.