2,4-二氯苯氧乙酸（英语：2,4-dichlorophenoxyacetic acid），也称2,4-二氯苯氧基乙酸，通称2,4-滴或2,4-D。植物生长调节剂和除草剂。纯的2,4-D为白色无臭晶体，难溶于水，易溶于有机溶剂。按植物种类的不同施用不同的剂量，可以促进插条生根，果实早熟，防止落花落果等作用。但是如果剂量使用不当，也会使植物受到严重伤害。

在越南战争中被美军作为落叶剂和除草剂所广泛使用的橙剂，它的的主要成分就是2,4-D和与其化学性质类似的2,4,5-三氯苯氧乙酸。

2,4-Dichlorophenoxyacetic acid (usually called 2,4-D) is an organic compound with the chemical formula C₈H₆Cl₂O₃. It is a systemic herbicide which selectively kills most broadleaf weeds by causing uncontrolled growth in them, but leaves most grasses such as cereals, lawn turf, and grassland relatively unaffected.