In contrast to the extensive studies of the electrochemical behavior of conventional cyclic S-8 molecules in Li-S batteries, there has been hardly any investigation of the electrochemistry of S chains. Here we use S chains encapsulated in single- and double-walled carbon nanotubes as a model system and report the electrochemical behavior of 1D S chains in Li-S batteries. An electrochemical test shows that S chains have high electrochemical activity during lithiation and extinctive electrochemistry compared with conventional S8. The confined steric effect provides Li+ solid-phase diffusion access to insert/egress reactions with S chains. During lithiation, the long S chains spontaneously become short chains, which show higher discharge plateaus and better kinetics. The unique electrochemistry of S chains supplements the existing knowledge of the S cathode mechanism and provides avenues for rational design of S cathode materials in Li-S batteries.