Abstract : The lasing characteristics of three-guide coupled rectangular ring laser containing active and passive sections were investigated numerically and experimentally. The rectangular laser cavity consists of four low-loss total internal reflection mirrors and an output coupler made from three passive coupled waveguides. The laser having active section lengths of 350 mm and total cavity lengths of 780 mm was fabricated. The lasing threshold current in the clockwise circulating direction is approximately 35 mA, while that in the counterclockwise circulating direction is around 40mA under continuous wave operation. The lasing characteristics are bidirectional operation of the single mode with a side mode suppression ratio better than 27 dB.