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SUMMARY Extracellular ATP (eATP) is known to act as a danger signal in both plants and animals. In plants, eATP is recognized by the plasma membrane (PM)‐localized receptor P2K1 (LecRK‐I.9). Among the first measurable responses to eATP addition is a rapid rise in cytoplasmic free calcium levels ([Ca²⁺]_cyt), which requires P2K1. However, the specific transporter/channel proteins that mediate this rise in [Ca²⁺]_cytare unknown. Through a forward genetic screen, we identified an Arabidopsis ethylmethanesulfonate (EMS) mutant impaired in the [Ca²⁺]_cytresponse to eATP. Positional cloning revealed that the mutation resided in thecngc6gene, which encodes cyclic nucleotide‐gated ion channel 6 (CNGC6). Mutation of theCNGC6gene led to a notable decrease in the PM inward Ca²⁺current in response to eATP. eATP‐induced mitogen‐activated protein kinase activation and gene expression were also significantly lower incngc6mutant plants. In addition,cngc6mutant plants were also more susceptible to the bacterial pathogenPseudomonas syringae. Taken together, our results indicate that CNGC6 plays a crucial role in mediating eATP‐induced [Ca²⁺]_cytsignaling, as well as plant immunity.