Abstract: A process for forming glass filaments by utilizing centrifugal force, in which compressed gas is injected from a position near an interior of a flame port frame of a fiberizing burner toward a throat portion of a discharge port of the burner at an acute angle relative to the direction of discharge of a flame stream from the discharge port, so that the compressed gas is mixed with combustion exhaust gas at an inlet portion of the throat portion, and the mixed gas is injected from the discharge port of the burner in a direction generally parallel to the direction of the generatrix of the outer peripheral surface of the peripheral wall, thereby forming primary filaments into fine secondary filaments.