The biophysical chemistry and solution dynamics of aqueous TMAO solutions have been extensively investigated from experimental viewpoints. Vibrational and nuclear magnetic resonance spectroscopy indicated that both the N + O -and CH 3 -groups of TMAO slow the dynamics of water molecules in a solution and that the N + O -groups have a notable ability to capture water molecules. Ab initio molecular dynamics (AIMD) simulations are essential for explaining the experimental results precisely, because of the fluctuating polarization interactions in the aggregated systems. Although there have been several sub-picosecond-order AIMD simulations, there have been no nanosecond-order AIMD simulations while reproducing the TMAO concentration and diffusion coefficients of water in deep-sea fishes.