The dynamics of polysulfide (PS) dissolution and re-deposition during electrochemical charge/discharge of the lithium-sulfur (Li–S) cell has been investigated in a quantitative manner based on in-operando transmission X-ray microscopy (TXM) analysis of dimensional variations of S particles in working cells that have been subjected to different depths of charge/discharge. Extensive shrinkage and expansion of S particles have been observed to result from PS dissolution and re-deposition, respectively. The dissolution rate of PS is found to have complex dependence on the Li content, being significantly higher for the stoichiometries of LiS8 and Li2S4 than those between Li2S8 and Li2S6. PS re-deposition is nucleation-limited, leading to considerable aggregation of the S-containing active mass and enormous dimensional variations of active particles. These two consequences may impose threat to the cycle stability of the electrode. Possible benefit of introducing favorable nucleation sites is discussed.