Thin and uniform Ti-containing silicalite-1 (TS-1) membranes were prepared for the first time by a microwave-assisted secondary growth method. The influence of synthesis temperature (150–200°C), duration (90–150min) and Ti concentration in the mother sol (molar ratio Si/Ti=16–100) on the membrane formation were studied. The quantity of Ti species inserted in the silicalite-1 network was found to vary with these parameters, as well as the membrane quality and performance. TS-1 membranes with a Si/Ti molar ratio in the range 25–40 were successfully prepared from mother sols with compositions in the range Si/Ti=16–100. An original parabolic evolution of membrane thickness vs. Si/Ti in the mother sol was evidenced, with a minimum thickness for Si/Ti around 50. In all cases Ti species were inserted within the zeolite network as far as no TiO 2 clusters were detected after the thermal treatment at 550°C. The membranes were typically 0.1–2μm thick top-layers and crystal preferential orientation varied from oblique- to c-crystal preferential orientation (CPO) when the temperature was increased from 160°C to 200°C. The permeances of He, N 2 , O 2 , CO 2 were high and lied in the range 1.9–7.48×10 −6 molm −2 s −1 Pa −1 when measured between 25°C and 200°C. The most selective membrane, prepared at 190°C during 120min with a molar ratio Si/Ti=75 in the mother sol, had an ideal selectivity of 40 for n/i-C 4 H 10 at 150°C and 105 for CO 2 /SF 6 at 25°C.