This study is concerned with fiber structure of new high-modulus type PBO fiber. Crystal modulus and molecular orientation change with stress was surveyed. Standard-modulus type PBO (AS) fiber has hysteresis effect to applied stress while high-modulus type PBO (HM) fiber shows reversible change. In order to raise actual PBO fiber modulus higher, nonaqueous coagulation process was adopted with conventional heat treatment. The fiber (HM+) so made gives 360 GPa in the Young's modulus and an absence of small-angle X-ray scattering pattern that is characteristic for aqueous-coagulated PBO fiber with heat treatment (Zylon(TM) HM). The crystal structure form and crystal size for the HM+ fiber are the same as those of the HM fiber.