Phraates II (also spelled Frahad II; Parthian: 𐭐𐭓𐭇𐭕 Frahāt) was king of the Parthian Empire from 132 BC to 127 BC. He was the son and successor of Mithridates I (r. 171–132 BC).

Because he was still very young when he came to the throne, his mother Rinnu initially ruled on his behalf. His short reign was mainly marked by his war with the Seleucid Empire, which under king Antiochus VII Sidetes (r. 138–129 BC) attempted to regain the lands lost to Phraates' father. Initially unsuccessful in the conflict, Phraates II managed to gain the upper hand and defeated Antiochus VII's forces, with the Seleucid ruler himself dying in battle or committing suicide. Phraates II afterwards rushed to the east to repel an invasion by nomadic tribes—the Saka and Yuezhi, where he met his end. He was succeeded by his uncle Artabanus I.

Phraátēs (Φραάτης) is the Greek form of the Parthian Frahāt (𐭐𐭓𐭇𐭕), itself from the Old Iranian *Frahāta- ("gained, earned"). The Modern Persian version is Farhād (فرهاد).

Phraates II was born in c. 147 BC; he was the son of Mithridates I, the fifth Parthian king, and a noblewoman named Rinnu, who was the daughter of a Median magnate.

Phraates succeeded his father in 132 BC; due to still being a minor, his mother ruled with him for a few months. Around this period, Phraates gave Darayan I kingship over the southern Iranian region of Persis. He also defeated and captured the ruler of Elymais Tigraios and appointed Kamnaskires the Younger to the throne of Elymais as a Parthian vassal. Continuing his father's plan, Phraates II had intentions to conquer Syria, and planned to use his captive—the former Seleucid king Demetrius II Nicator—as an instrument against his brother—the new Seleucid king Antiochus VII Sidetes (r. 138–129 BC). According to the 2nd-century Roman historian Justin, Demetrius attempted to escape captivity twice, both times during the reign of Phraates. The first attempt occurred after Mithridates I's death, with the second attempt happening a few years after:

Following his [Mithradates I's] death, despairing of [ever] returning [home], Demetrios, who did not bear his captivity, and was weary of a life, albeit opulent, as a private person, contemplated in secret a flight to (his) kingdom. […] But Phrahates, who had succeeded to Arsaces [Mithradates I], brought back the fugitive [Demetrios], who had been overtaken by the rapidity of the horsemen. Being taken to the king… he [the king] sent Demetrios, severely chastised, back to his wife in Hyrcania, and ordered that he be kept in confinement. Then, time having gone by… he [Demetrios] took flight again with the same friend as companion, with equal misfortune, he was seized near the borders of his kingdom, and conducted again to the king who regarded him with ill will; he was removed from his presence. Thereupon, as a grant to his wife and children he was sent back to Hyrcania, the city of his [former] imprisonment…

— Justin, Epitome of the Philippic History of Pompeius Trogus, 38.9.4–9

Antiochus, well-aware of Phraates II's plan to use his brother against him, invaded the Parthian realm in 130 BC to thwart it. He was reportedly well received by many magnates, who joined him. After three battles he reclaimed Babylonia. At the same time, the eastern Parthian frontier was invaded by nomads. Antiochus' forces wintered in Parthian territory; before spring, he entered into negotiations with Phraates II. Self-confident after his victories, Antiochus demanded not only the release of Demetrius, but also the return of the all lost lands and renewal of tribute fees. Phraates II, offended by the reply, broke off the negotiations and prepared for battle.