We studied an use of the continuous wave(cw) lasers (infrared and ultra-violet) to the laser angioplasty by in vitro and an animal experiment in vivo. The use of the cw lasers provides an advantage of the reliable laser energy delivery by a thin flexible fiber. We had already reported the ablation characteristics and the fiber delivery capability of the CO laser. In this paper, we describe another interesting cw laser for the laser angioplasty. The ablation characteristics of the uv Ar laser of which wavelength was approximately 350nm was studied. To develop an operation procedure of the angioscopic laser angioplasty, the animal experiments in vivo have been done under a visualization by a thin laser angioscope catheter with the CO laser irradiation. The advantage of the visualization during the laser angioplastic procedures are discussed.