Acetylcholine (ACh) signaling in the basolateral amygdala (BLA) has been implicated in salience-related processing and associative learning, yet the circuit mechanisms that regulate its dynamics remain poorly understood. Here we show that BLA ACh dynamically represented salience. In the mouse nucleus accumbens (NAc), D1-expressing medium spiny neurons (MSNs) selectively promote, whereas D2-expressing MSNs selectively suppress, ACh release in the BLA but not in the cortex or hippocampus. NAc D1 and D2 MSNs regulate BLA ACh by disinhibiting and inhibiting cholinergic neurons in the substantia innominata (SI), respectively. Axon terminals of D1 and D2 MSNs in the SI exhibit differential responses to salient stimuli and modulate BLA ACh dynamics. Closed-loop optogenetic manipulations of NAc D1 and D2 projections to the SI have opposing effects on associative learning. Our findings uncover an unconventional role of striatal MSNs in modulating behavioral significance through the regulation of salience-related amygdalar ACh activity.