This work aims to reveal the strong influence of nanostructures on the light absorption property of and perovskite mixture. Three nanostructures, i.e., nanoparticles (S1), ultrapure nanorods (S2), and ultrasmall nanorods (S3), were studied: S1 was selected as a baseline; S2 and S3 were synthesized from S1 by using modified hydrothermal processes. Mesoporous thin films were spin-coated from solutions containing these nanorods and nanoparticles (S1 as baseline). Organic–inorganic hybrid perovskite was then incorporated into these mesoporous thin films. Optical absorption results showed that the perovskite mixture with ultrasmall nanostructures (S3) has significantly higher optical absorption coefficient. Finite-difference time domain models were built based on three distinct nanostructures of and mixtures fabricated (S1 to S3) to understand their optical absorption properties. Our work is promising to fabricate nanostructures, as a backbone structure, for a series of applications including photovoltaics and photodetection.