In this paper, we propose a novel rateless coding scheme for dynamic decode-and-forward (DDF) relaying in wireless relay networks. The proposed rateless code is developed to overcome the high error floor problem caused by the Luby Transform (LT) code-based encoding scheme in Raptor codes. The improvement is achieved by providing each symbol with approximately equal protection in the belief propagation (BP) decoding, and by designing a special full rank parity-check matrix in the encoding process. Simulation results show that the proposed scheme considerably outperforms the existing rateless coding scheme in wireless relay networks with DDF relaying protocols.