Molecular processes in large uniaxial stretching of amorphous polyethylene are studied by molecular dynamics simulation. An initial isotropic amorphous sample nearly free from internal strain is made at 200 K with the aid of Monte Carlo chain generation followed by relaxation of residual strain by the molecular dynamics simulation. The initial sample is cooled to 100 K, and then subjected to a uniaxial stress of 2000 bar. Three independent simulations of uniaxial deformations are made for different draw directions. The system is rapidly elongated at a rate of about 3 x 10(9) s-1 irrespective of draw direction. The temperature of the system increases markedly during deformation. The temperature rise is very pronounced in the initial stage of deformation, but it slows down markedly around 180 K. Such a change in the rate of temperature rise as well as other anomalies observed in the potential energies of the system are suggested to be closely related to the reported glass transition around T(g) = 180 K. Bond orientation develops continuously by stretching. It is especially conspicuous below 180 K, where the system is considered to be in the glassy state and the molecule does not have sufficient mobility to adjust its conformation to the thermal equilibrium condition. The molecular process of large deformation is found to be divided into three stages : the first stage of breaking interchain binding, probably without serious intrachain deformation; the second stage up to T(g), where a rapid temperature rise occurs accompanied by appreciable void and fibre formation; and the third stage above T(g), where the further development of voids and fibres becomes very conspicuous due to the increased chain mobility.