Objective:To explore the effect of butylphthalide on oxidative stress and cognitive function in old obstructive sleep apnea hypopnea syndrome (OSAHS)patients.Method:A total of 90 old OSAHS patients with cognitive impairment were choosed with Polysomnography(PSG). By random number table method OSAHS patients were randomly divided into non-invasive ventilator group (n=30), butylphthalide with non-invasive ventilator group(n=30) and treatment group of butylphthalide(n=30). Non-invasive ventilator group was given continuous positive airway pressure treatment for three months, butylphthalide with non-invasive ventilator group accepted oral butylphthalide therapy and continuous positive airway pressure treatment for three months, treatment group of butylphthalide only accepted oral butylphthalide therapy for three months. Cognitive function of three groups wered observed by the Montreal cognitive assessment scale (MoCA) before and after treatment, at the same time, the changes of serum superoxide dismutase(SOD) and malondialdehyde(MDA) were detected by immunoenzyme-linked adsorption.Result:The differences of serum SOD and MDA before treatment among the three groups were not statistically significant (P>0.05). Compared with before treatment, the level of serum SOD increased and the level of MDA decreased in the three groups (P<0.05). Compared with non-invasive ventilator group after treatment,the level of SOD increased and the level of MDA decreased in butylphthalide with non-invasive ventilator group (P<0.05), the level of SOD decreased and the level of MDA increased in treatment group of butylphthalide (P<0.05). Compared with treatment group of butylphthalide after treatment, the level of SOD increased and the level of MDA decreased in butylphthalide with non-invasive ventilator group (P<0.05); The scores of MoCA on cognitive function before treatment in the three groups was not statistically significant (P>0.05). After treatment the scores of MoCA on cognitive function in the three groups were higher than those before treatment (P<0.05). Compared with non-invasive ventilator group after treatment, the scores of MoCA increased in butylphthalide with non-invasive ventilator group (P<0.05),the the scores of MoCA decreased in treatment group of butylphthalide (P<0.05). Compared with treatment group of butylphthalide after treatment, the scores of MoCA increased in butylphthalide with non-invasive ventilator group (P<0.05).Conclution: Butylphthalide can improve the activity of antioxidant enzymes in the serum of old patients with OSAHS, inhibit the oxygen free radical and lipid peroxidation and to a certain extent improve the cognitive function.