Directly compressed mini tablets were produced containing either hydroxypropylmethylcellulose (HPMC) or ethylcellulose (EC) as release controlling agent. The dynamics of water uptake and erosion degree of polymer were investigated. By changing the polymer concentration, the ibuprofen release was modified. In identical quantities, EC produced a greater sustaining release effect than HPMC. Different grades of viscosity of HPMC did not modify ibuprofen release. For EC formulations, the contribution of diffusion was predominant in the ibuprofen release process. For HPMC preparations, the drug release approached zero-order during a period of 8 h. For comparative purposes, tablets with 10 mm diameter were produced.