Blind detection of space-time block coding (STBC) scheme without channel state information (CSI) was proposed in , which suffered a performance penalty of 3 dB compared to the coherent detection. Compared to the differential STBC, this scheme requires no differential encoder at the transmitter. In this paper, we present a new blind detection method for STBC. We show that by defining an intermediate variable, the STBC encoder can be modeled as a Markov process and described by a trellis. Coding gain is revealed in the STBC with QPSK and 8PSK modulations. The Viterbi decoder can be applied for STBC at the receiver without the knowledge of CSI. The new scheme can perform better than the conventional blind detection of STBC. Furthermore, the new blind decoder of STBC is used in the iterative blind detection scheme of coded STBC.