Renal cyst enlargement especially in polycystic kidney disease (PKD) is driven by P2Y receptor‐mediated and cAMP‐mediated chloride secretion into cyst lumen. This study aimed to determine the effect of an anti‐asthmatic drug montelukast, cysteinyl leukotriene (CysLT) 1 receptor antagonist, on renal cyst progression and to investigate underlying mechanisms of such an effect. In MDCK cyst model, montelukast (50 μM) inhibited forskolin‐induced cyst growth and cyst formation by 80%. This effect was not reversed by leukotriene D4 co‐incubation. In addition, zileuton, an inhibitor of leukotriene synthesis, had no effect on cyst growth. As analyzed by short‐circuit current measurements, acute treatment with montelukast (50 μM) inhibited ATP (P2Y agonist)‐induced chloride secretion by 50%, with no effect on cAMP‐induced chloride secretion. Similarly, prolonged treatment with montelukast (50 μM, 24 h) significantly inhibited ATP‐induced chloride secretion. Furthermore, montelukast had no effect on cell viability. Our study indicates that montelukast inhibits MDCK cyst progression by attenuating purinergic signaling in these cells. Therefore, montelukast represents a promising candidate drug for PKD therapy.This work was supported by the Faculty of Science and Medical Scholars Program, Mahidol University.