As a final stage of cell signal transduction, secretory cells release hormones by exocytosis. Before secretory granules contact with the cell membrane for fusion, an actin network barrier must dissociate as a prelude. In order to elucidate dynamical behaviors of secretory granules in actin network, in vitro assembly and disassembly processes of actin networks were examined by means of dynamic light-scattering spectroscopy. We studied actin polymerization in the presence of chromaffin granules isolated from bovine adrenal medullae, and found that the entanglement of actin filaments rapidly formed cages which confined granules in them. We also studied the effect of gelsolin, one of the actin-severing proteins, on the network of actin filaments performed in the presence of chromaffin granules. It turned out that the cages which confined granules rapidly disappeared when gelsolin was added in the presence of free Ca2+ ions. Semiquantitative analyses of dynamic light-scattering spectra permitted us to estimate the changes in the mobility (or translational diffusion coefficient) of chromaffin granules in the actin network with its assembly and Ca2+-dependent disassembly by gelsolin. Based on the present results and some pieces of evidence in literature, a model is proposed for biophysical situations before, during, and after an exocytotic event.