The present work deals with the effect of the constrained volume given by crosslinked chitosan (CHI) as a sphere on the in vitro CaC0(3) crystallization. Crosslinked CHI was obtained with formaldehyde (FA), glutaraldehyde (GA), epichlorhydrine (EPCH) and poly (propylene glycol) diglycidyl ether (PPDGE) as crosslinking agents. Determination of swelling percentage (%) of the crosslinked CHI spheres was carried out in TRIS buffer at pH 9. Spheres of high molecular weight were prepared using drops of CHI solution on NaOH. In vitro CaC0(3) crystallization using gas-diffusion method was done. In addition, a synthetically sulphonated containing polymethylsiloxane (S-PMS) was used as modifying additive on the CaC0(3) crystals growth in a confined space of CHI. The degree of the crosslinking altered the diffusion of C0(2) gas through the CHI spheres during the CaC0(3) crystallization resulting in different and specific crystals morphologies