Abstract We have investigated dynamics of deuterated p -nitroaniline (pNA- d ) molecules in FSM-16 mesoporous silica (FSM) and FSM modified with trimethylethoxysilane (C1FSM) with different loading amounts ranging from 10 to 50 mass% by means of solid-state NMR. We have measured temperature dependence of 2 H NMR spectra and spin-lattice relaxation times ( T 1 ) as well as 13 C magic-angle-spinning (MAS) NMR spectra. The 2 H and 13 C MAS NMR spectra indicate that there are two modes of motions; an isotropic motion and a fast wobbling one. The rates of the wobbling motion are estimated from the 2 H T 1 results. pNA- d molecules in the FSM/pNA- d sample of 10 mass% undergo the wobbling motion at the low temperatures, whereas the isotropic motion is relatively suppressed at the high temperatures. In the samples of 20 and 30 mass% the wobbling motion is suppressed at the low temperatures, whereas the isotropic motion is enhanced at the high temperatures. The above changes further proceed in the sample of 50 mass%. The temperature dependences of 2 H spectra in C1FSM/pNA- d of 13 and 20 mass% are similar to those of FSM/pNA- d of 20 and 30 mass%. C1FSM/pNA- d of 30 mass% shows spectra intermediate between FSM/pNA- d of 30 mass% and FSM/pNA- d of 50 mass%. We have proposed “three-layer model” to explain the above NMR results.