Lysine methylation is one of the most important modification, which is regulated by histone lysine methyltransferases and histone lysine demethylases. Lysine-specific demethylase 1 (LSD1) specifically demethylates mono- and dimethyl-lysine on histone H3 (H3K4Me/Me₂, H3K9Me/Me₂) to control chromatin structure, resulting in transcriptional repression or activation of target genes. Furthermore, LSD1 is overexpressed in various cancers. Therefore, LSD1 inhibitors would be not only potential therapeutic agents for cancers but also chemical tools to research biological significance of LSD1 in physiological and pathological events. However, known assay methods to date have some inherent drawbacks. The development of simple method in detecting LSD1 activity has been indispensable to identify useful inhibitors. In this study, we designed and synthesized artificial substrates based on inhibitors of LSD1 to examine LSD1 activity by an absorption increment.