Hierarchical two-dimensional (2D) lamellar zeolites represent a young emerging field and a novel expression of the zeolite frameworks. Accompanied with synthesis and catalytic performance investigation, assessment on the local environment and catalytic behavior of acid sites in 2D zeolites are needed. Here, we described the local environment of Lewis acid sites and evaluated catalytic activities of external acid sites (i.e. sites on external surface and in mesopores) in 2D lamellar titanium silicalite-1 (TS-1) zeolites. For comparison purpose, four TS-1 zeolites, including 3D TS-1, multilamellar 2D TS-1 without pillarization and with pillarization by silica and silica/titania, respectively, were prepared. The local environment of Ti-sites, including coordination status of Ti-atom, speciation of hydroxyl (-OH) group that hints degree of confinement, acid site strength and accessibility, was collectively assessed by spectroscopic and organic base titration measurements. Kinetic studies of cyclooctene (C8H14) epoxidation with hydrogen peroxide (H2O2) discerned catalytic activity of external Ti-sites that decreased with increasing mesoporosity due to decrease in site confinement. Display omitted •External Lewis acid sites in 2D TS-1 zeolites were quantified.•2D TS-1 zeolites have high density of isolated surface silanol and titanol groups.•Reactivity of external sites decreases with increasing mesoporosity in 2D TS-1.•Decrease in reactivity of external sites is caused by loss of partial confinement.•Kinetic decoupling of epoxidation pathways enabled catalytic behavior assessment.