Objectives Spinal glycinergic mechanisms inhibit the micturition reflex, and administration of glycine inhibits bladder activity in rats. Therefore, we examined whether dietary glycine would improve storage symptoms in urological outpatients. Methods We enrolled 20 participants (16 men and four women) with an overactive bladder symptom score (OABSS) ≥ 3. All participants took 3 g of glucose (placebo) twice a day for the first four weeks, then 3 g of glycine twice a day for the next four weeks. We evaluated blood pressure, international prostate symptom score (IPSS), nocturia quality of life (N-QOL) score, OABSS, frequency of urination, sleep latency, time to first nighttime void, bladder pain, global self-assessment (GSA) evaluated urinary symptom improvement, and adverse events. Results Glucose administered as a placebo improved urinary frequency, urine force on the IPSS, and five of the 13 items on the N-QOL. However, compared to the results before and after glucose administration, glycine treatment decreased the number of nocturnal voids, urgency, and total score for urine storage items on the IPSS. It also reduced blood pressure and improved IPSS-QOL. For the OABSS, improvements with glycine were noted in the number of nocturnal urinations, urinary urgency, urge incontinence, and total score. For the N-QOL, eight of 13 items, and the total score, improved. The actual number of nighttime urinations, sleep latency, latency to first nighttime urination, bladder pain, and GSA also improved. There were no adverse events. Conclusions Glycine might improve urine storage symptoms, cardiovascular function, pain, and sleep.