Immunolocalization is a necessary technique in the study of chromosome structure and function. It can provide important information for better understanding the relation between epigenetic modifications and chromosome condensation. In this protocol, we describe a way to localize and detect the distribution of histone H3 methylated at lysine 9 (inactive heterochromatin) in embryos at a period of 14 day-after-pollination (DAP). The protocol allows the observation of somatic cells in mitotic chromosome spreads.