Abstract: In modern wireless communication systems, multiple-antenna-transmitting in association with Orthogonal Space-Time Block Code (OSTBC) is a key technology to improve communication rate, reliability, and decoding complexity. In this paper, a modulation identification algorithm is proposed which is well suitable for the Multiple Input Single Output (MISO)-OSTBC system. First, the MISO system is transformed into a Multiple Input Multiple Output (MIMO) system by reshaping the received data. Then, maximum likelihood based approach is used to identify the modulation. Simulations validate the effectiveness of the proposed algorithm.