In 1554, when the father of Ujimasa, Ujiyasu, established an alliance Ko So Sun Sangoku Domei (tripartite of Kai-Sagami-Suruga alliance) with Shingen TAKEDA and Yoshimoto IMAGAWA, Ujimasa took a daughter of Shingen TAKEDA, Obai-in, for his lawful wife.
天文23年（1554年）、父・氏康が武田信玄、今川義元との間で甲相駿三国同盟を成立させると、武田信玄の娘・黄梅院(北条氏政正室)を正室に迎えた。