Purpose: It is known that a moderate to large volume of alcohol produces deterioration in obstructive sleep apnea (OSA), however, no consensus has been achieved with respect to the influence of a moderate volume of alcohol on mild to moderate OSA. In this study, we investigated the influence of alcohol on OSA-associated parameters in healthy middle-aged males drinking a moderate volume of alcohol (<1 g alcohol/kg bodyweight per day). Methods: Subjects were 23 healthy males (mean age of 46.0) with a habitual ingestion of moderate amounts of alcohol. Respiratory sleep parameters were measured through the fitting of an Apnomonitor III (Chest Inc.) and portable sleep monitoring device (Actiwatch: AMI Inc.) to subjects on three nights; an alcohol-free night, a night on which they drank alcohol with dinner, and a night on which they drank alcohol within 30 minutes before retiring to bed. The measurements were categorized into the early and late halves of assumed sleep for analysis. Results: The apnea-hypopnea index was significantly higher when drinking alcohol before retiring [mean (SD): 7.8 (8.2) events/hour] than the values on the alcohol-free day [2.9 (4.5) events/hour] and when drinking alcohol with dinner [3.8 (5.3) events/hour]. Furthermore, drinking alcohol before retiring resulted in lower arterial blood oxygen saturation (SpO2) during the early half of sleep [94.8 (1.4) %] when compared to the values on the alcohol-free day [95.7 (1.3) %] and drinking alcohol with dinner [95.4 (1.6) %]. In addition, the percentage of time with SpO2 <92% (hypoxic event) during the early half of sleep [4.9 (9.3) %] was significantly higher than the values on the alcohol-free day [1.2 (1.8) %] and when drinking alcohol with dinner [1.4 (1.8) %]. Conclusion: These results suggest that moderate ingestion of alcohol within 30 minutes before retiring aggravates OSA-associated parameters in healthy males.