低音长笛是木管乐器，属于长笛的一种变种。它是1920年代才发明的新变种乐器，，于爵士音乐上开创无簧片类木管器乐的低音区域，但现时普及度不高，通常只限于长笛合奏团才会使用。而在管乐团中，低音长笛的音色很容易就被单簧管类的乐器所盖过，因此亦同样罕见。

乐器的英文名称「Bass Flute」，在20世纪初曾被英国作曲家视为「中音长笛」（Alto Flute），例如霍尔斯特的《行星组曲》标示为「Bass Flute　in G」，现时已经再没有类似的情况发生。

低音长笛为移调乐器，采用高音谱号，实际音比记谱音低1个八度，它可吹奏音域和长笛相同，但一般而然，低音长笛不会吹奏吹过谱记音A₆，原因是它的高音并不准确，一般以长笛代替便可。

The bass flute is the bass member of the flute family. It is in the key of C, pitched one octave below the concert flute. Because of the length of its tube (approximately 146 cm), it is usually made with a "J" shaped head joint, which brings the embouchure hole within reach of the player. It is usually only used in flute choirs, as it is easily drowned out by other instruments of comparable register, such as the clarinet.