The purpose of this mSR study is to investigate the volume fraction of antiferromagnetic (AF) ordered regions and the temperature where AF order is developed, TN, in the electron-doped high-Tc cuprate La1.8Eu0.2CuO4-xFx with the Nd2CuO4-type (so-called T-type) structure. Recently, we succeeded in synthesizing undoped superconductor T'- La1.8Eu0.2CuO4 sample which has higher Tc ~ 24 K than the conventional T'-La1.8Eu0.2CuO4 samples with Tc ~ 15 K and 20 K. Moreover, we also successfully synthesize the electron-doped T'-La1.8Eu0.2CuO4-yFy samples by the F-substitution. Therefore, mSR measurements using these samples are expected to give us significant information on the relationship between the Cu-spin correlation and superconductivity in undoped T'-La1.8Eu0.2CuO4. The information will be important to clarify the mechanism of the superconductivity in undoped T-Ln2CuO4.