Chaotic systems possess many features useful for cryptography. In the paper, a random bit generator based on two chaotic systems exponentially cross-coupled with each other is presented. Afterwards, four tests: mono-bit test, serial test, Poker test and auto-correlation test are employed to evaluate the randomness of the generator. At last, we analyze the linear complexity of the generated sequences, the key space and the efficiency. All the experiments show that the proposed generator holds satisfactory properties.