Dextran was produced using in 3% calcium alginate immobilized and free cells of L. mesenteroides ATCC 10830 (NRRL B-512 F). Information about the molecular structure of the produced polymers using size exclusion chromatography and on-line low angle laser light scattering (SEC/LALLS) detection was obtained. Dextran formed outside the beads by immobilized cells possesses an average molecular weight of about 1.84 x 10⁷ daltons. Average molecular weight of dextran formed by free cells, however, was 1.32 times (2.43 x10⁷ daltons for free cells) that formed by immobilized cells. Determination of the qualitative branching parameters (G^-1 _v and G_M) of dextran formed by both cultures shows that branching of dextran produced by free cells was also higher than that produced by immobilized cells in calcium alginate.