Pressure and temperature region of cubic BN growth was determined using hexagonal BN starting material and solvent having Ca3B2N4 composition. The growth region of cubic BN was bounded by two lines namely the phase boundary line between hexagonal BN and cubic BN (P(GPa)=T(°C)/465+0.79) and minimum liquid forming temperature line (approx. 1120 °C between 4 and 6 GPa). Threshold pressure of cubic BN formation, which has been reported previously at approximately 5 GPa, was not observed. It was confirmed that cubic BN was precipitated even at 3.6 GPa. The results revealed that re-crystallized hexagonal BN was precipitated in advance of cubic BN nucleation below approximately 5 GPa in the stable pressure and temperature region of cubic BN. Cubic BN crystals were precipitated in the re-crystallized hexagonal BN after approximately 2 h of incubation time.