Superhydrophobic membranes composed of an organic-inorganic hybrid polymer, namely polycarbosilane (PCS) with Mw of 4-8.9 ×10 3 , were formed on a mesoporous γ-Al 2O3-modified α-Al2O3 porous support. Under dry condition at 50 • C, the supported PCS membranes exhibited H2 permeance of 1.1-1.6 ×10 −6 mol⋅m −2 ⋅s −1 ⋅Pa −1 and H2/N2 selectivity of 9.7-12.6 together with unique H2/He selectivity of 1.4-1.6. Even under saturated humidity at 50 • C, H2 permeance remained at 7.7 ×10 −8 mol −1 m −2 s −1 Pa −1 with improved H2/N2 selectivity of 26. Moreover, when the measurements were performed using a H2-N2 (2:1) mixed feed gas as a simulated syngas produced by novel solar hydrogen production systems, the H2 permeance almost unchanged, while the N2 permeance was below the limit of detection. These results revealed a great potential of PCSs to develop novel H 2selective membranes for purifying solar hydrogen under high-humidity conditions around 50 • C. Further study on the gas permeation behaviors of He, H2 and N2 suggested that the enhanced H2/N2 selectivity under the highhumidity conditions could be explained by the synergistic effect of preferential H 2 permeation through the dense PCS network governed by the solid state diffusion mechanism and blockage of N 2 permeation through micropore channels within the PCS network by the permeate H2O-induced plugging at around the hetero interface between the superhydrophobic PCS and highly hydrophilic γ-Al 2O3.