The complexity and diversity of microstructure involved in titanium alloys make it rather difficult to quantitatively describe microstructural evolution. In the present study we focus on microstructure evolutions during heating and isothermal holding considering the effect of the initial microstructure on the dissolution kinetics of alpha-phase. Quantitative microstructure characterizations have been realized. At first, in situ high energy X-ray synchrotron and electrical resistivity was used to follow the dissolution kinetics of  phase. Then, an algorithm capable of quantifying various microstructural data was developed. The microstructural features include the amount of nodular and lamellar alpha-phase, the mean equivalent diameter and the aspect ratio of nodular alpha- phase. This algorithm was applied to TA6V4 samples submitted to different isothermal temperature. The initial microstructure of the samples was either a duplex microstructure (lamellar and nodular alpha-phase) or a nodular microstructure. The dissolution kinetics of alpha-phase was compared with the equilibrium calculations predicted by ThermoCalc. It appears clearly that a large amount of phase is dissolved on heating in spite of a rapid heating rate.