Recently, several alkylamine hydrates have been studied in an effort to reveal the structural transitions from semi-to 'canonical' clathrate hydrate in the presence of secondary guest molecules. Trimethylamine (TMA) is known to form the semi-clathrate hydrate, and it has been reported that the structural transition of the TMA semi-clathrate hydrate may not occur in the presence of hydrogen gas as a secondary guest molecule. In this study, we investigate the structural transition of TMA hydrate by CH4 gas. Powder X-ray diffraction was used to analyze the crystal structure of a binary (TMA + CH4) clathrate hydrate, and the results showed that the structural transition from semi-to cubic structure II hydrate can occur in the presence of methane gas. C-13 solid-state NMR and Raman spectroscopy were used to confirm the distribution of guest molecules. Finally, we measured the phase equilibrium conditions of a binary (TMA + CH4) clathrate hydrate. The guest-induced structural transformation in amine semi-clathrate hydrates can provide useful insight into the complex nature of the host guest inclusion system, and these results can be applied to research on potential gas storage and transportation areas.