Interstitial cystitis (IC) is a chronic inflammatory bladder disorder with recurring severe pain, lacking timely diagnostic and therapeutic options. Here, we propose a unitary theranostic nanocluster-antibody-drug conjugate (NADC) by covalently placing dihydroorotate dehydrogenase inhibitors (DHODHi) and ultrasmall gold quantum clusters (AuQCs) on a nerve growth factor (NGF) antagonistic antibody with simultaneous X-ray computed tomographic and near-infrared fluorescence imaging contrasts. Combining anti-inflammatory effects from all individual components, intravesical NADC specifically homed to mucosal lesions with NGF overexpression in voided bladder and capably alleviated inflammation in chronic, acute, and prophylactic IC models of rats, as revealed by behavioral and pathological evaluations. Transcriptomics unveiled cytokine modulation and concomitant inhibition of perturbed IL-17, NF-{kappa}B, TNF, and JAK-STAT signaling pathways. Notably, NADC indirectly remodeled the host bladder microbiota by differentially varying anti-inflammatory and pro-inflammatory bacteria diversities. Distinct from conventional nanoparticles conjugated with antibodies and drugs, NADC relies on the antibody framework, outperforms clinical standard-of-care agents, and represents an emerging category of precision theranostic agents with translational potential for IC theranostics in clinical practice.