Abstract: A modified method was used for the separation and purification of Anabaena cylindrica nitrogenase, based upon which a further study on the cross-reactivity between Fe-protein from A. cylindrica and MoFe-protein from Azotobacter vinelandii was made. Results indicated that these two heterologous components were able to give an effective cross-reaction and showed a relatively strong nitrogenase activity. The specific activities of acetylene reduction and H2-evolution contributed by cross-reacting heterologous components were as high as 83.8% and 66.7%, respectively, of that produced by algal homologous complementary response. In comparison with the kinetics of the algal homologous complementary reaction, it was found that the optimum molar ratio of Fe-protein to MoFe-protein for heterologous cross-reaction is much higher (5:1), the time course for tooth reactions being approximately the same. Discordant with the current conception, our findings demonstrate that the Fe-protein of A. cylindrica can form effective complexes with the MoFe-protem of Azotobacter.