Nicostratus, (gr. Nikostratos), an Athenian general, the son of Diitrephes.

We first hear of him in 427 BC. The struggle between the oligarchical and democratical parties in Corcyra had commenced, when Nicostratus arrived from Naupactus with twelve ships and a body of 500 Messenians. Through his mediation a compact was entered into between the contending parties, and a defensive and offensive alliance with the Athenians was formed. As Nicostratus was about to depart the leaders of the commonalty persuaded him to leave five of his vessels, promising to man five for him instead. On board these they attempted to place their enemies, but the latter fled for refuge to the temple of the Dioscuri. Nicostratus strove to allay their fears, but to no purpose. About 400 of the party took refuge in the temple of Here, and were thence carried over to the island of Ptychia. A few days afterwards, before the Athenians had departed, tile Peloponnesian fleet under Alcidas and Brasidas arrived. The democratical party were thrown into consternation. Tile Athenian squadron set out in good order to meet the enemy, and skilfully sustained the attack of thirty-three vessels of the Peloponnesian fleet; and Nicostratus was beginning to repeat the manoeuvres of Phormio, which had been attended with such success off Naupactus, when the remaining part of the fleet, having routed the Corcyraeans, advanced against the Athenians, who were compelled to retire. (Thuc. iii. 75, &c.)

In 424 BC, Nicostratus was one of the colleagues of Nicias in the expedition in which Cythera was taken. (Thuc. iv. 53, &c.) He was one of the Athenians who took the oaths to the year's truce concluded between Sparta and Athens (Thuc. iv. 119); and later in the same year was the colleague of Nicias in the expedition to Chalcidice. (Thuc. iv. 129, 130).

In 418 BC, Nicostratus and Laches led a body of 1000 heavy-armed soldiers and 300 cavalry to Argos, accompanied by Alcibiades as ambassador. The Athenian troops, accompanied by the allies of Argos, proceeded to attack Orchomenos, which made no resistance. From Orchomenos, having been joined by the Argives, the combined forces proceeded against Tegea. Agis marched to protect the place, and in the battle which ensued near Mantineia Nicostratus and his colleague were both slain. (Thuc. v. 61-74).