Three nanosized ZSM-5 zeolites were successfully prepared from reactive gels\t\t\t\t\twith the same Si/Al ratios by different synthetic procedures that included the\t\t\t\t\tuse of tetrapropylammonium hydroxide or n-butylamine as a template and a seeding\t\t\t\t\tmethod that did not use an organic additive. The effect of the synthetic method\t\t\t\t\ton the physicochemical properties of the prepared samples was investigated by\t\t\t\t\tXRD, XRF, XPS, N2 physisorption, SEM, TEM,\t\t\t\t\t\t27Al MAS NMR, NH3-TPD, and\t\t\t\t\t\tPy-FTIR. The catalytic performance of the\t\t\t\t\tnanosized ZSM-5 zeolites in the alkylation of naphthalene with methanol was\t\t\t\t\tcompared. The prepared samples were phase-pure, highly crystalline ZSM-5\t\t\t\t\tzeolites, but they had different bulk and surface Si/Al ratios as well as\t\t\t\t\ttextural and acidic properties. The study of the prepared catalysts in\t\t\t\t\tnaphthalene methylation revealed that both the acid characteristics of the ZSM-5\t\t\t\t\tnanosized zeolites and their textural properties were responsible for their\t\t\t\t\tactivity in the reaction. A difference in the composition of\t\t\t\t\tmonomethylnaphthalenes and dimethylnaphthalenes was attributed to the ability of\t\t\t\t\tthe catalyst to isomerize the primary reaction products on acid sites located on\t\t\t\t\tthe external surface of the zeolite crystals. 2,7-DMN was found to be the\t\t\t\t\tpreferred reaction product over 2,6-DMN when formed at pore entrances to ZSM-5\t\t\t\t\tchannels due to the differences in their dimensions. In contrast,\t\t\t\t\t2,6-dimethylnaphthalene could be produced on weaker external Brønsted acid\t\t\t\t\tsites, which are hydroxyls attached to octahedral Al atoms. The presented\t\t\t\t\tresults show that the method used to synthesize nanoscale ZSM-5 zeolites is a\t\t\t\t\tcritical factor that determines the physicochemical properties and catalytic\t\t\t\t\tperformance of the resulting crystals.