Cathodoluminescence (CL) was used to investigate the mode and compositional zoning of plagioclase in fine-grained metapelites of the Imjingang Belt, Korea. Minute, untwinned grains of plagioclase are indistinguishable from quartz under the polarized light microscope. However, distinct colour and intensity of the CL of plagioclase permit not only rapid identification but also characterisation of its compositional zoning on a thin-section scale without extensive compositional mapping. The abundance of plagioclase in the analysed samples suggests that this mineral could be more common in low- to medium-grade metapelites than previously recognized. CL colours of plagioclase vary from dull green through green to bright greenish yellow as the An content increases. Furthermore, CL petrography suggests the syn-kinematic growth of outer part of plagioclase (An51-69). Hence, CL microscopy can provide a wealth of information not only for deciphering P-T-t paths but also for microfabric analysis of fine-grained schists.