The purpose of this study was to investigate the morphological and histological changes in the urethra in beagle dogs after intraurethral Er:YAG laser irradiation in nonablative mode to confirm the safety of this therapy. Six 2-year-old healthy female virgin beagle dogs (13 +/- 1.51 kg) were used in this study. The animals were divided into 2 groups: the sham group, which received sham treatment (n = 3) involving insertion of an intraurethral cannula and laser delivery handpiece into the urethra without laser irradiation, and the experimental group (n = 3), which received intraurethral Er:YAG laser irradiation. The laser irradiation parameters were set according to clinical criteria (4 mm spot size, 1.5 J/cm(2), 1.4 Hz, and 4 pulses) in nonablative mode. All animals received three sequential sessions at 4-week intervals. Urethrography and urethroscopy were performed in the 12th week and 13th week, respectively, after the first treatment. After urethroscopy, the animals were sacrificed, and urethral tissue was harvested for histological investigations. All procedures were performed under general anesthesia (40 mg/kg 3% sodium pentobarbital, i.v.). Transforming growth factor beta 1 (TGF-beta 1) and alpha-smooth muscle actin (alpha-SMA) expression levels were measured to evaluate the biochemical characteristics of the scar. Urethral stricture was not found by urethrography or urethroscopy in either group. Urethral epithelium thickness and collagen expression under the urethral mucosa were significantly increased in the experimental group compared with the sham group. However, there were no significant differences in TGF-beta 1 and alpha-SMA expression between the experimental group and sham group (p > 0.05). Urethral stricture is not found in beagle dogs after clinically relevant intraurethral nonablative mode Er:YAG laser irradiation. Proliferation of urethral collagen and the urethral mucosa may be one of the mechanisms by which urine leakage symptoms can be improved.