To explore the relation between DNA base composition and the optimal single-strand conformation polymorphism (SSCP) electrophoretic temperature (T-s), we analyzed DNA base composition and T, of 24 DNA fragments from different genes and found that T-S was positively correlative with the ratio of base C/base A. T-S could be estimated by the formula T-S = [80 x C/(A + 1)]/({2.71 + [C/(A+ 1)]}. T-S could be increased dramatically by the complementary sequences in both 5'-and X-ends of a DNA single-strand.