Callose (β-1,3-glucan) is one of the cell wall polymers that has multiple biological functions and plays an important role in plant growth and development processes. Callose is the cytological marker of reproductive cells in young ovules of most sexually reproducing angiosperms, whereas in ovules of apomictic plants, callose deposition does not occur or is altered. Aniline blue staining is one of the methods to detect callose. Aniline blue fluorochrome binds preferentially to β-1,3-glucans and is widely used to visualize callose in various plant tissues. Here, we describe an easy-to-perform procedure for fluorescent imaging of callose in whole-mount ovules using aniline blue-stained fixed flowers. This procedure enables rapid and precise detection of callose in ovules in order to determine and compare the pattern of its distribution during early sexual and apomictic reproductive processes.