MOF-5@SiO2 and IRMOF-10@SiO2 with different pore sizes and shell thicknesses were synthesized by a layer-by-layer method and used to explore the effects of pore size on dye adsorption behaviour. The characterization results indicated that shell thickness could dramatically influence pore structure. Mesopores and macropores in MOFs@SiO2 existed when the synthetic cycles were less than 10, while micropores could be obtained when MOFs@SiO2 were prepared after 20cycles. The adsorption kinetic and isotherm results showed that adsorption of basic fuchsin onto MOF-5@SiO2 increased but the adsorption capacities decreased with increasing shell thickness. The adsorption rate of basic fuchsin on IRMOF-10@SiO2 was lower and the adsorption capacity was higher than that of MOF-5@SiO2. Meanwhile, the adsorption rates of IRMOF-10@SiO2 decreased, but the capacities increased as the shell thickness increased. Moreover, Fourier transform infrared and X-ray photoelectron spectroscopy were used to investigate possible adsorption mechanisms. The results suggested that basic fuchsin could enter the pores of IRMOF-10@SiO2 but could not enter MOF-5@SiO2 due to the size-exclusion effect.