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The circadian clock allows plants to actively adapt to daily environmental changes through temporal regulation of physiological traits. In response to drought stress, circadian oscillators gate ABA signalling, but the molecular mechanisms remain unknown, especially in crops. Here, we investigated the role of soybean circadian oscillators GmLCLa1, GmLCLa2, GmLCLb1 and GmLCLb2 in leaf water stress response. Under dehydration stress, the GmLCL quadruple mutant had decreased leaf water loss. We found that the dehydration treatment delayed the peak expression of GmLCL genes by 4 hr. In addition, the circadian clock in hairy roots also responded to ABA, which led to a free‐running rhythm with shortened period. Importantly, in the gmlclq quadruple mutant, diurnal expression phases of several circadian‐regulated ABA receptor, ABA catabolism and ABA signalling‐related genes were shifted significantly to daytime. Moreover, in the gmlclq mutant leaf, expression of GmPYL17, GmCYP707A, GmABI2 and GmSnRK2s was increased under water dehydration stress. In summary, our results show that GmLCLs act as negative regulators of ABA signalling in leaves during dehydration response. We investigated the molecular characteristics and the physiological function of circadian oscillators in soybean. We found the GmLCL quadruple mutant had decreased leaf water loss under dehydration stress, and GmLCLs act as negative regulators of ABA signalling in leaves during dehydration response. [ABSTRACT FROM AUTHOR]