We compared the optical properties of the trimeric photosystem (PS) I complexes of the primordial cyanobacterium Gloeobacter violaceus PCC 7421 with those of Synechocystis sp. PCC 6803. Gloeobacter violaceus PS I showed (1) a shorter difference maximum of P700 by approximately 2 nm, (2) a smaller antenna size by approximately 10 chlorophyll (Chl) a molecules and (3) an absence of Red Chls. The energy transfer kinetics in the antennae at physiological temperatures were very similar between the two species due to the thermal equilibrium within the antenna; however, they differed at 77 K where energy transfer to Red Chls was clearly observed in Synechocystis sp. PCC 6803. Taken together with the lower P700 redox potential in G. violaceus by approximately 60 mV, we discuss differences in the optical properties of the PS I complexes with respect to the amino acid sequences of core proteins and further to evolution of cyanobacteria.