Objective　To investigate the efficacy of alarm treatment in a sample of China monosymptomatic nocturnal enuresis (MNE) children and adolescents with smaller than expected bladder capacity (EBC) for age. Methods  Fifteen MNE patients with a smaller than age-expected BC and without nocturia were included. All the patients were treated with enuretic alarm and water restriction 2 hours before sleep. All patients were followed up monthly. A success criterion was defined as “14 consecutive dry nights” after successive 2-3 months treatment. A relapse criterion was defined as “more than two wet nights every two weeks” after therapy discontinuation. The relapsed patients were treated with enuretic alarm and followed up again. Results  The patients consisted of 9 boys and 6 girls. The mean age was 9.76±4.24 years (6-15 years). Thirteen patients were successfully cured after three months treatment. Two patients discontinued the treatment and received the treatment of desmopressin. Five patients relapsed and received the enuresis alarm treatment again. Four patients had never relapsed, and one failed. The cure rate was 80%. Conclusions  The enuretic alarm device is effective on MNE patients with a smaller than age-expected BC and without nocturia.