Korean Red Ginseng (KRG) is a functional food and has been well known for keeping good health due to its anti-fatigue and immunomodulating activities. However, there is no data on Korean red ginseng for its preventive activity against acute respiratory illness (ARI). The study was conducted in a randomized, double-blinded, placebo-controlled trial in healthy volunteers (Clinical Trial Number: NCT01478009). Our primary efficacy end point was the number of ARI reported and secondary efficacy end point was severity of symptoms, number of symptoms, and duration of ARI. A total of 100 volunteers were enrolled in the study. Fewer subjects in the KRG group reported contracting at least 1 ARI than in the placebo group (12 [24.5%] vs 22 [44.9%], P = 0.034), the difference was statistically significant between the two groups. The symptom duration of the subjects who experienced the ARI, was similar between the two groups (KRG vs placebo; 5.2 ± 2.3 vs 6.3 ± 5.0, P = 0.475). The symptom scores were low tendency in KRG group (KRG vs placebo; 9.5 ± 4.5 vs 17.6 ± 23.1, P = 0.241). The study suggests that KRG may be effective in protecting subjects from contracting ARI, and may have the tendency to decrease the duration and scores of ARI symptoms.