Direct contact membrane distillation (DCMD) is a promising method for water purification and it is essential to fabricate membranes with high porosity, narrow pore distribution and high surface hydrophobicity. In this study, carbon-nanotubes (CNTs) with two surface functionalization, i.e., silanization and fluorosilanization, were compounded with polyvinylidene fluoride (PVDF) to prepare electrospun composite nanofiber membranes for DCMD. The effects of CNT surface functionalization on CNT dispersity and membrane pore size, porosity, hydrophobicity, and DCMD performance were investigated. The results showed that CNTs improved the membrane hydrophobicity and surface functionalization of CNTs furthered this improvement. It was found that membranes with co-functionalized CNTs achieved the highest distillate flux (~ 45 Lm-2h-1) and salt rejection (~ 99.99 %) among the tested membranes. This flux was 14 % and 46 % higher than the fluxes on the membranes with unfunctionalized-CNTs and without CNTs, respectively. Characterizations suggested that the superior performance was attributed to the co-functionalization improved dispersity of the CNTs, high porosity (~ 85.5%), large mean pore size (~ 0.89 µm) and surface superhydrophobicity (contact angle of ~153 º) of the membrane. This work implied that co-functionalization of CNTs is an avenue of great potential to improve the performance of PVDF membranes in DCMD application.