固定低音（ground bass，或意大利语的basso ostinato，又译顽固低音），是指一组在音乐中反复出现的低音组，低音部不断重复一些短小的主题动机，或者完全重复一个固定的旋律。

顽固低音的技法是指在作品中从头到尾反复着相同的低音组，通常在固定低音变奏曲中使用。巴洛克时期舞曲中的夏康舞曲（恰空，Chaconne）以及帕夏卡利亚（帕萨卡里亚，Passacaglia），就是一种类似顽固低音变奏曲的技法编写的作品。

In music, an ostinato [ostiˈnaːto] (derived from Italian: stubborn, compare English: 'obstinate') is a motif or phrase that persistently repeats in the same musical voice, usually at the same pitch. Well-known ostinato-based pieces include both classical compositions such as Ravel's Boléro and popular songs such as Donna Summer and Giorgio Moroder's "I Feel Love" (1977) and The Verve's "Bitter Sweet Symphony" (1997).