- Birth: 1548
- Death: 1606
- Other names: Sakikabara Heishichi, Sakikabara Koheita
- Titles: Shikibu-Taiyu, Daijuji
- Distinction: Tokugawa retainer
- Sons: Tadamasa, Sakikabara Tadanaga [榊原忠長, 1585-1604], Yasukatsu [榊原康勝, 1590-1615]
Yasumasa was the 2nd son of Sakikabara Nagamasa [榊原長政] and was born at Ueno in Mikawa Province. He served Tokugawa Ieyasu from childhood and rose to become one of his chief retainers. He was married to the daughter of Osuga Yasutaka.
Yasumasa, though young, was first recognized by Ieyasu for his talents in the 1564 suppression of the Mikawa monto and was granted the use of the charactor '康' (Yasu) in his name. Although the second son in the family, Yasumasa succeeded his father, the reasons for this remaining unclear. He came of age in 1566 and became one of Tokugawa Ieyasu's guard captains [旗本部隊の将].
He served in a notable capacity at the Battle of Anegawa (along with Honda Tadakatsu providing an attack on the flank of the Asai forces dangerously pressing Oda Nobunaga) and was present at Nagashino, helping to defeat Naito Masatoyo. He was present at the Battle of Mikagahara, the Battle of Nagashino, and the capture of Takatenjin Castle.
During the Komaki Campaign (1584) Yasumasa wrote up a statement attacking Toyotomi Hideyoshi and calling on support for the cause of Oda Nobuo and later accompanied Ieyasu to Osaka to meet with Hideyoshi himself (1586). During this trip he was awarded with the honorific title Shikibu-taiyu. In 1590 he participated in the Odawara Campaign. Following Ieyasu's move to the Kanto Region that same year, Sakikabara was given the castle of Tatebayashi and made the head of a committee responsible with assigning fiefs. While Ieyasu was away on Kyushu during Hideyoshi's Korean Campaigns Sakakibara acted as one of Tokugawa Hidetada's councilors. When the Sekigahara Campaign began in 1600, Yasumasa was assigned to Tokugawa Hidetada's army and was thus present for the siege of Ueda Castle in Shinano Province. He was afterwards given a 100,000-koku fief at Tatebayashi in Kozuke Province. He died at Tatebayashi in the 5th month of 1606.
Yasumasa was succeded by his 3rd son Yasukatsu, his 2nd son, Tadanaga, having died in 1604. One of his natural daughters married Ikeda Toshitaka [池田利隆] and another married Sakai Tadayo [酒井忠世]. An adopted daughter married Kizuregawa Yoshichika (喜連川義親正, 1599-1627)
The Sakikabara remained one of the Tokugawa's most trusted retainer houses into the Edo Period.