The aim of this work is to study the kinetics of martensitic transformations realized under isothermal holding conditions in the Ti40.7Hf9.5Ni44.8Cu5 alloy. It is shown that in the alloy Ti40.7Hf9.5Ni44.8Cu5, the forward martensitic transformation realizes under isothermal conditions within and outside the martensitic transformation temperature range. It is found that the volume fraction of the isothermally transformed martensite increased with time. The value of isothermally transformed new phase depends on holding temperature and its maximum value (80 %) is observed at a holding temperature equal to Ms.