Highly porous hydrophobic hollow fiber membranes with high porosity and sandwich trilayer structure were specially designed to meet the requirements of direct contact membrane distillation (DCMD). Poly(vinylidene fluoride) (PVDF)/Cloisite clay composite hollow fibers were fabricated based on the dry-jet wet phase inversion mechanism by using water as both the external and internal coagulants. Membrane void fraction of up to 90% can be produced to improve the fibers' thermal insulation and reduce vapor transport resistance. The fiber inner surface was full of streaky pores with pore size less than 1.0 mu m in diameter, while the pores on the fiber outer surface were much smaller, less than 50 nm in diameter. This demonstrates that membrane pores fabricated at a nanoscale can achieve high water vapor permeation flux with 100% salt rejection. For example, the fabricated PVDF/clay composite hollow fiber was tested by desalinating a 3.5 wt % NaCl solution and permeation flux as high as 79.2 kg/(m(2).h) (calculated on the fiber outer diameter) was achieved at the inlet temperatures of 81.5/17.5 degrees C. The performance shows almost no decay during 220-h continuous tests. The addition of clay particles may enhance the tensile modulus and improve long-term stability compared to those fibers without particles.