Fucoxanthin chlorophyll a/c-binding proteins (FCPs) are unique light harvesters for some photosynthetic organisms. There were several reports for the alterations of FCPs in response to light conditions. Here, we present the spectral profiles and excitation dynamics of novel FCP complexes isolated from the diatom Chaetoceros gracilis. Under a red-light condition, C. gracilis cells expressed three types of FCP complexes, two of which are very similar to FCP complexes found in the white-light grown cells, and one of which is the novel FCP complex. The combination of steady-state absorption and fluorescence spectra and time-resolved fluorescence spectra revealed that, compared to other types of FCP complexes, the novel FCP complexes exhibited red-shifted absorption and fluorescence spectra and fast decay of excitation. This finding will provide new insights into not only the light-harvesting strategies of diatoms but also the diversity of light adaptation machinery for photosynthetic organisms.