Overreduction states of photosystem I (PSI) cause PSI photoinhibition. To examine the degree of PSI photoinhibition, changes in its electron transport activity and core-subunit content were evaluated. In contrast, the involvement of peripheral subunits, such as the light-harvesting complex I (LHCI), is less discussed in PSI photoinhibition. Here, we aimed to elucidate whether the light-harvesting functions of LHCI are altered by PSI photoinhibition in rice leaves. To this end, a new method to estimate the functional antenna size of the PSI-LHCI complex was developed using a far-red light-dependent absorption change in the oxidized reaction center chlorophyll (P700 ⁺) in intact leaves, and the obtained kinetics were analyzed using the double Gompertz model. Subsequently, our original parameter, k_fast (Far Red-Photon Flux Density) ^-1, showed a linear response to leaf LHCI content, and the parameter decreased with a decrease in P700 content by PSI photoinhibition in leaves. Furthermore, we found that the susceptibility of LHCI to PSI photoinhibitory treatment decreased with increasing in growth light intensity. Our results suggest that LHCI is a target of PSI photoinhibition, as well as the core-subunits, and rice plants can lower the risk of LHCI photoinhibition through light acclimation responses.