Morphology: Adult specimens typically have mean snout-vent lengths of 55.3 ±3.3 mm and mean weights of 10.9 ±1.8 grams.

They have well-developed nuptial pads with enlarged prepollex on the distal phalanx of finger I. Cloacal openings are displayed ventrally and extend anteriorly below the thighs.

Small light greenish-white spots are present on the posterior parts of the flank anterior to the groin.

Both sexes have yellowish-whitish upper lips and webbing between the toes that are red to purple shaded.

Some coloration differences in sexes: In green males the area between dorsolateral folds appears darker than females due to blackish spiculae being present.

Supra-ocular yellowish stripes are visible on females but not males due to lack of spiculae obscuring them.

B. occidentalis is primarily live along permanent rivers which allows for longer larvae period and therefore allows metamorphs to reach larger size because of the lower evo-transpiration rate.

Males aggregate in spaced out choruses after sunset into late night in shallow slow-moving pools along the edges of streams.

Calls of the male Boophis occidentalis are emitted at irregular intervals and are composed of unharmonious notes with no clearly arranged regular series.