Sulfur (S) encapsulated in porous carbon nanofibers (CNFs) was synthesized via electrospinning, carbonization and solution-based chemical reaction-deposition method. The chemical reaction-deposition strategy provides intimate contact between the S and the CNFs. This would not necessarily be the case for other reported methods, such as ball milling and thermal treatment. These novel porous carbon nanofiber-sulfur (CNF-S) nanocomposites with various S loadings showed high reversible capacity, good discharge capacity retention and enhanced rate capability when they were used as cathodes in rechargeable Li/S cells. We demonstrated here that an electrode prepared from a porous CNF-S nanocomposite with 42 wt% S maintains a stable discharge capacity of about 1400 mA h g(-1) at 0.05 C, 1100 mA h g(-1) at 0.1 C and 900 mA h g(-1) at 0.2 C. We attribute the good electrochemical performance to the high electrical conductivity and the extremely high surface area of the CNFs that homogeneously disperse and immobilize S on their porous structures, alleviating the polysulfide shuttle phenomenon. SEM measurements showed that the porous CNF structures remained nearly unchanged even after 30 cycles' discharging/charging at 0.05 C.