Eucalyptus optima is a tree or mallet that typically grows to a height of but does not form a
lignotuber. Young plants have stems that are square in cross-section, with wings on the corners and dull greyish green, egg-shaped to lance-shaped leaves that are long and wide. Adult leaves are the same shade of dull bluish or greyish green on both sides, lance-shaped, long and wide, tapering to a
petiole long. The flower buds are arranged in leaf
axils in groups of seven or nine on an unbranched, usually down-turned
peduncle long, the individual buds on
pedicels long. Mature buds are oval to oblong, long and wide with a beaked to horn-shaped
operculum. Flowering has been observed in May, August and September and the flowers are pale yellow. The fruit is a woody, cup-shaped, hemispherical or urn-shaped
capsule long and wide with the valves protruding strongly above the rim. ==Taxonomy and naming==