二十碳四烯酸（英语：Eicosatetraenoic acid，简称ETA）是一种有20个碳原子和4个双键的多元不饱和脂肪酸。

二十碳四烯酸有两种同分异构体，其中主要的异构体有两种，它们都是必需脂肪酸：

有些化学文献把花生四烯酸解释为所有二十碳四烯酸，但是大多数文献解释花生四烯酸只是“全 顺5,8,11,14-二十碳四烯酸”。

Eicosatetraenoic acid (ETA) designates any straight chain 20:4 fatty acid.

Two isomers, both of them essential fatty acids, are of particular interest:

Some chemistry sources define 'arachadonic acid' to designate any of the eicosatetraenoic acids. However, almost all writings in biology, medicine and nutrition limit the use the term 'arachidonic acid' to all-cis 5,8,11,14-eicosatetraenoic acid (ω-6).