Allergic rhinitis (AR) has considerable impact on the general health of individuals. Therefore, treatment trials should include an evaluation of quality of life. We aimed to determine changes in the quality of life of moderate/severe AR patients treated with standard treatment in addition to dialyzable leukocyte extract (DLE), a peptide-based immunomodulator. In a prospective, non-controlled trial, DLE was added to the standard treatment regimen for patients with moderate/severe AR. DLE was administered orally at 2 mg per day for 5 days, followed by 4 mg per week for 5 weeks, and then 2 mg per week for 5 weeks. The primary endpoints were overall improved Standardized Rhinoconjunctivitis Quality of Life Questionnaire (RQLQ) scores, domain scores, and individual item scores of 0.5 points or higher. Statistical significance was defined asP< .05. Thirty patients (50% female) aged 14 to 60 years old (33.4 ± 11.9) were enrolled in this study. The mean overall basal quality of life score was 3.41 ± 1.22. After 11 weeks, the mean RQLQ score was 1.74 ± 1.09 (P< .0001; 95% confidence interval [CI], 1.05-2.33), and all the domain scores improved (daily activitiesP< .001, 95% CI 0.91–2.15, sleepP< .001, 95% CI 0.9–2.26, non-hay fever symptomsP= .001, 95% CI 0.51–1.82, practical problemsP< .001, 95% CI 1.55–2.85, nasal symptomsP< .001, 95% CI 1.36–2.67, ocular symptomsP< .001, 95% CI 1.05–2.17, emotionalP< .001, 95% CI 1.23–2.55). Each of the 28 individual item scores on the RQLQ showed clinical (minimal important difference [MID] ≥ 0.5) and statistical (P< .05) improvements. DLE might be a beneficial adjuvant treatment for AR. Our results provide preliminary data for future research.Clinical trials registration ID: NCT02506998