Laparoscopic surgery is one of the most established application of the surgical robot, and many commercial surgical robot systems are available. These laparoscopic surgical robots have remote center of motion (RCM) mechanism to prevent the motion of the surgical tool in an unwanted direction. In addition, various surgical instruments with high maneuverability and precision in a narrow space are available with these robots. Using these advantages, studies have been made to apply laparoscopic surgical robots to microsurgery, but they are limited by the high price and large size of the robots. In this paper, we introduce the development of a compact surgical robot arm for microsurgery, such as anastomosis, which can be used with the instruments of a commercial laparoscopic surgical robot. This robot arm utilizes a spherical serial RCM mechanism to ensure that translation of the surgical instrument is always directed toward the surgical site, improving stability and accuracy. In addition, the surgical instrument of a commercial laparoscopic surgical robot Revo-i, can be attached and driven by the arm. Design and manufacturing of the microsurgical robot arm is presented.