This paper aims to report the fabrication of biodegradable thin films with micro-domains of cylindrical nanochannels through the solvent-induced microphase separation of poly(L-lactide)-block-poly(ethylene glycol)-block- poly(L-lactide) (PLA-b-PEG-b-PLA) triblock copolymers with different block ratios. In our experimental scope, an increase in each of the block lengths of the PLA and PEG blocks led to both a variation in the average number density (146 to 32 per 100 mu m(2)) and the size of the micro-domains (140 to 427 nm). Analyses by atomic force microscopy (AFM) and fluorescence microscopy indicated that the hydrophilic PEG nanochannels were dispersed in the PLA matrix of the PLA-b-PEG-b-PLA films. We demonstrated that the micro-domain morphology could be controlled not only by the block length of PEG, but also by the solvent evaporation conditions.