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Objective: To screen phytochemicals in ethanolic leaf extracts of Phyllanthus amarus collected from three different geographical zones in Nigeria and evaluate their effects on larva and adult of Anopheles gambiae. Methods: The sample extracts of Phyllanthus amarus prepared with ethanol solvent were tested against Anopheles gambiae at two important developmental stages of its life cycle using slightly modified WHO protocols. Results: Alkaloids, saponins, tannins, flavonoids, glycosides, phenols, and terpenes were detected in each extract. Among these samples, the extract from northwest exhibited the highest larvicidal activity (LC50=263.02 ppm), followed by southeast and southwest extracts (LC50=288.40 and 295.12 ppm, respectively after 48 h), while the extract from southwest exhibited the highest adulticidal activity (LC50=275.42 ppm), followed by northwest and southeast extract (LC50=301.99 and 316.22 ppm, respectively after 24 h). A 50％ larva mortality was almost attained at 600 ppm after 48 h duration of exposure to the northwest extract. Conclusions: The tested samples possess strong larvicidal and adulticidal property against Anopheles gambiae which depends on their chemical composition and localities of collection. Further studies are needed to explore the insecticidal activity against a wider range of mosquito species, and to identify active ingredient(s) of the extract responsible for such activity.