Objective To explore the risk factors causing tetany in patients with hyperventilation syndrome. Meth?ods A total of 103 patients with hyperventilation syndrome treated in our hospital were included in this study. According to whether there was tetany, patients were divided into tetany group and non-tetany group. Values of gender, age, electrolyte, pH and p(CO2) were analysed between two groups. The factors of P<0.1 were engaged in binary Logistic regression. Logistic regression (Forward Wald) was used to analyze the risk factors of tetany in patients with hyperventilation syndrome. Re?sults In 103 patients there were 70 patients with tetany (68%), 33 patients without tetany(32%). The serum K+, serum phos?phorus and p(CO2) values were significantly lower in tetany group than those of non-tetany group (P<0.01), while the pH value was significantly higher in tetany group than those of non-tetany group (P<0.01). There were no significant differences in gen?der, age, serum Na+, serum Cl-, serum calcium (bound calcium and ionized calcium), ionized calcium and serum Mg2+levels be?tween two groups (P>0.05). It was revealed that the younger age, the lower level of the serum K+, serum phosphorus and p(CO2) were the risk factors of tetany through binary Logistic regression analysis. Conclusion The risk factors of tetany in patients with hyperventilation syndrome include younger age, lower level of serum K+and serum phosphorus and reduced p(CO2).