Ca2+ sparks are well known to be essential for controlling the relaxation of cerebral artery SMCs; however, the functional importance of this local Ca2+ signaling in other types of SMCs remains to be determined. Thus, the aim of this study was to investigate the role of Ca2+ sparks in airway SMCs. Our data reveal that spontaneous Ca2+ sparks could activate spontaneous transient inward currents (STICs) at the resting membrane potential and spontaneous transient outward currents (STOCs) at more positive membrane potentials in mouse airway SMCs. Application of ryanodine to block ryanodine receptors (RyRs) abolished spontaneous Ca2+ sparks without altering the whole-cell cytosolic Ca2+ levels in single airway myocytes and decreased the resting muscle tension in isolated airway rings, whereas activation of RyRs with a low concentration of caffeine had opposite effects. Iberiotoxin, a selective blocker of big-conductance Ca2+-activated K+ channels, eliminated STOCs, but did not affect either spontaneous Ca2+ spark activity or resting muscle tension. In contrast, NPPB, an inhibitor of Cl− channels, reduced resting muscle tension. The effect of NPPB was prevented in the presence of the selective voltage-dependent Ca2+ channel blocker nifedipine. We have also found that the activity of Ca2+ sparks in single asthmatic mouse airway SMCs and in-vivo airway resistance in asthmatic mice were significantly increased. Interestingly, ryanodine caused a stronger relaxation in asthmatic airway smooth muscle. Taken together, these findings suggest that spontaneous Ca2+ sparks can activate Ca2+-activated Cl− channels and then generate STICs, causing membrane depolarization, opening of voltage-dependent Ca2+ channels, extracellular Ca2+ influx and contraction in airway SMCs. Moreover, Ca2+ sparks and attendant STICs are both increased in asthmatic airway SMCs, which may contribute to asthmatic airway hyperresponsiveness.