The melting temperatures (T-m) of branched polyethylene (B-PE) have been measured over the pressure range up to 2 GPa by use of a high-pressure X-ray diffraction apparatus. The T-m-P curve for B-PE is expressed as (T-m/T-m,T-o)(c)=(P+P-o)/a where T-m,T-o is the T-m at atmospheric pressure, c=4.788, P-o=280.2MPa and a=P-o +0.1 MPa. The T-m of B-PE increases with increasing pressure monotonically, and T-m=310 degrees C at 2 GPa. The X-ray diffraction peaks corresponding to the spacing d = 3.84 Angstrom for the (110) lattice plane of the orthorhombic B-PE crystal do not change with increasing temperature below 1.85 GPa but d values for the (200) lattice plane increase with increasing temperature. The thermal properties of a B-PE melt crystallized at various high pressures above 1.0 GPa have been measured at atmospheric pressure, and four endothermic peaks are observed for the sample melt crystallized at 800 MPa. The entropies of fusion Delta S-F Of B-PE and linear polyethylene (L-PE) at pressures up to 200 MPa have been determined based on the Clausius-Clapeyron equation and P-V-T data by O. Olabisi and R. Simha (Macromolecules, 1975, 8, 206), and Delta S-F for B-PE is much smaller than for L-PE.