The nuclear factor of activated T-cells (NFAT) is a calcium (Ca²⁺)-dependent transcription factor that has been reported to regulate the expression of smooth muscle contractile proteins and ion channels. Here we report that large conductance Ca²⁺-sensitive potassium (K⁺) (BK) channels and voltage-gated K⁺ (K_V) channels may be regulatory targets of NFATc3 in urinary bladder smooth muscle (UBSM). UBSM myocytes from NFATc3-null mice displayed a reduction in iberiotoxin (IBTX)-sensitive BK currents (I_BK), a decrease in mRNA for the pore-forming -subunit of the BK channel, and a reduction in the BK channel density compared to myocytes from wild-type mice. TEA-sensitive K_V currents (I_Kv) were elevated in UBSM myocytes from NFATc3-null mice, as was mRNA for the Shab family member, K_V2.1. Despite the upregulation in K_V current, bladder strips from NFATc3-null mice displayed an elevated contractile response to electrical field stimulation (EFS) relative to strips from wild-type mice, but this difference was abrogated in the presence of the BK channel blocker IBTX. These results support a role for the transcription factor NFATc3 in regulating UBSM contractility, primarily through an NFATc3-dependent increase in BK channel activity.