With the help of KLTER/ME and KLPS in Woraksan, we have surveyed monthly diversity and seasonal prevalence of Macrolepidoptera in Wol-ak-san [Mt.] for the period of five months from May to September since 2005. Since 2007, to reduce variation, we chose two monitoring points, instead of one, for each of the three representative vegetations: Quercus mongolica-, Quercus variabilis- and Pinus densiflora-formations, abbreviated as QM, QV and PD, respectively, and collected exclusively larger moths with bucket-type of light traps for quantified survey. In 2009, as a result, QV showed higher species diversity and specimen number than QM or PD although the differences between QV and QM are subtle. The number of individuals collected may not be a good indicator, e.g., Idaea biselata collected in QM in June was over 200 in 2007, which is more than twice the number of specimens in all other sites per month, while the number in 2008 was dropped to only 10 specimens. In 2009, they became a dominant species again, showing biennial dominancy trend. It also seems that we are experiencing major decline of specimen numbers: 651 specimens collected in 2009 while 874 specimens collected in 2008, which was already a big reduction compared to over 2500 specimens in 2007