Yukmijihwangtang (YM), a boiled extract of medicinal plants, has been prescribed for patients with kidney dysfunction in Korea; however, the mechanism underlying its therapeutic effects has not been fully elucidated. This study was conducted to evaluate the beneficial effects on bladder function by using modified YM (M-YM), which included Ulmi radicis cortex in addition to the six traditional medicinal plants in YM. Bladder irritation of the rats was caused by intravesical instillation of HCl. The animals were divided into six groups: sham group, cystitis-injury group with no treatment, cystitis-injury group with prednisolone treatment (5 mg/kg), and cystitis-injury with M-YM treatment (100, 200 or 500 mg/kg groups). Whole bladders were collected at day eight after injury. Samples were analyzed by histological and immunological examinations. An in vitro study was performed to determine whether M-YM extracts inhibit lipopolysaccharide (LPS)-induced nitric oxide (NO) production and IκB phosphorylation in a human uroepithelial cell line of T24 cells. Administration of M-YM notably improved bladder histological changes, and suppressed IL-6/TNF α production and IκB phosphorylation in a rat model of chronic cystitis. M-YM also inhibited LPS-induced NO production and IκB phosphorylation in T24 cells. This study suggests that administration of M-YM might be an applicable therapeutic traditional medicine for the treatment of interstitial cystitis.