Slowly degradable copolymers of L-lactide and ε-caprolactone can provide long-term delivery and may be interesting as alternative release systems of cyclosporine A (CyA) and rapamycin (sirolimus), in which available dosage forms cause a lot of side effects. The aim of this study was to obtain slowly degradable matrices containing immunosuppressive drug from PLACL initiated by nontoxic Zr[Acac]₄. Three kinds of poly(L-lactide-co-ε-caprolactone) (PLACL) matrices with different copolymer chain microstructure were used to compare the release process of cyclosporine A and rapamycine. The influence of copolymer chain microstructure on drug release rate and profile was also analyzed. The determined parameters could be used to tailor drug release by synthesis of demanded polymeric drug carrier. The studied copolymers were characterized at the beginning and during the degradation process of the polymeric matrices by NMR spectroscopy, GPC (gel permeation chromatography), and DSC (differential scanning calorimetry). Different drug release profiles have been observed from each kind of copolymer. The correlation between drug release process and changes of copolymer microstructure during degradation process was noticed. It was determined that different copolymer composition (e.g., lower amount of caprolactone units) does not have to influence the drug release, but even small changes in copolymer randomness affect this process.