The synthesis of hematite mesocrystals with a tunable hierarchical nanostructure plays a critical role in the construction of improved functional materials. We have demonstrated that two recombinant collagen proteins can be used as superior biotemplates to produce hematite mesocrystals with easily tunable hierarchical nanostructures under hydrothermal conditions. Compared with previously reported proteins, collagen is able to regulate the hierarchical structures of hematite mesocrystals with a much lower concentration, and collagen can produce a richer diversity of hierarchical nanostructures, adding two novel diamond-like and sphere-like structures in addition to the three previously reported structures (spindle-like, olive-like, and ellipsoidal-like). The distinct (Gly-X-Y)n amino acid sequence pattern and triple helix structure may provide unique capability for collagen in protein-templated biomineralization. Our studies have indicated that sequence and structural differences in proteins may lead to a plethora of novel nanostructures, which would significantly contribute to the development of improved inorganic nanomaterials.