Studing the binding of the 5-Iodopyrimdines by human serum albumin we obtained the following conclusions; 1. The more strong electron donating groups in the molecule of 5-Iodopyrimidines, the larger the binding force with human serum albumin. This trend seems to be attributed by increase of polarization of the electron donating groups in 5-Iodopyrimidines molecule. 2. The binding force of 5-Iodopyrimidines by human serum albumin is increased with the pH increasing could be occurred the configurational changes of human albumin mole-cule, and this new binding sites of human serum albumin molecule would form the intermolecular complex with 5-Iodopyrimidines molecule more strongly.