Blend films were prepared from poly(L-lactide) (PLLA) and poly(Ε-caprolactone) (PCL) with different PLLA contents [XPLLA (w/w) = PLLA/(PCL + PLLA)] by the solution-casting method and their hydrolysis behaviors were investigated up to 20 months in a phosphate-buffered solution of pH 7.4 at 37℃ by gel permeation chromatography, tensile testing, differential scanning calorimetry, and gravimetry. Polarizing microscopic observation and dynamic mechanical analysis revealed that PCL and PLLA were phase-separated in blend films before hydrolysis. The mass remaining, molecular weight, and tensile strength of the blend films with XPLLA of 0.5 and 0.75 decreased more rapidly by hydrolysis than those of the nonblended PLLA, while the elongation at break of the blend film of XPLLA = 0.25 decreased the slowest. The rate constant for hydrolysis (k) calculated from the Mn change during hydrolysis was higher for blend films of XPLLA = 0.5 and 0.75 than those expected from k of nonblended PLLA and PCL. The melting temperature (Tm) of PLLA in the blend and nonblended films of XPLLA = 0.5, 0.75, and 1 decreased from 179 to 161, 160, and 175℃ upon hydrolysis for 20 months, respectively, while that for XPLLA = 0.25 slightly increased from 176 to 177℃. On the other hand, Tm and the crystallinity of PCL was significantly increased by hydrolysis for 20 months, irrespective of XPLLA.