We report a different type of microvascular end-to-side anastomosis using "open-Y" technique to increase small recipient vessel size and provide eversion of the vessel ends in end-to-side anastomosis. The purpose of this study was to compare the effectiveness of this technique with conventional end-to-side vessel anastomosis. Twenty rats were used to assess the open-Y technique in end-to-side anastomosis between carotid arteries and external jugular veins and another 20 rats constituted the control group in which conventional end-to-end anastomoses were performed. Statistically, the results at 1 hour and 2 weeks after the procedures favored the open-Y technique. When used in end-to-side anastomosis, the open-Y technique both provides eversion and increases the diameter of the vessel, which in turn case the procedure and provide a higher rate of patency especially in vessels with a diameter of 0.5 mm.