It was the first shipment of a recently approved package of US military aid for Ukraine, and included ammunition for "front-line defenders".
The delivery followed US Secretary of State Antony Blinken's visit to Kyiv this week, where he warned of a tough response if Russia was to invade.
Moscow has denied any plans to attack or invade Ukraine.
US President Joe Biden approved the $200m (£147.5m) security support package in December.
The US embassy in Kyiv said the shipment demonstrated its "firm commitment to Ukraine's sovereign right to self-defense".
"The United States will continue providing such assistance to support Ukraine's Armed Forces in their ongoing effort to defend Ukraine's sovereignty and territorial integrity against Russian aggression," it wrote on Facebook.
Ukrainian Defence Minister Oleksiy Reznikov thanked the US for the aid.
Russia has seized Ukrainian territory before - Crimea, in 2014 - and the head of the military alliance Nato has warned there is a real risk of a fresh conflict in Europe after an estimated 100,000 Russian forces amassed on the border.
Moscow has denied it is planning an invasion, but President Vladimir Putin has issued demands to the West which he says concern Russia's security, including that Ukraine be stopped from joining Nato.
He also wants Nato to abandon military exercises and stop sending weapons to eastern Europe, seeing this as a direct threat to Russia's security.