Rheumatoid arthritis (RA) is a destructive autoimmune disease that seriously affects human health. Due to the lack of a cure for RA, a good prognosis largely depends on early diagnosis and effective treatment monitoring of RA. Therefore, the development of fluorescent probes capable of real-time detection of RA is of great significance. Dual-state emission (DSE) molecules can emit light in both dilute solution and solid state, making them ideal fluorophores for constructing fluorescent probes. However, there are currently no reports of DSE molecule-based fluorescent probes for RA imaging. Herein, we report a fluorescent probe MQP-Boc based on a novel DSE molecule for effective RA imaging. MQP-Boc selectively responds to viscosity with sensitive fluorescence changes at 667 nm and is mitochondria targetable. Cell imaging studies show that MQP-Boc can detect changes in mitochondrial viscosity and perform long-term imaging of mitochondria, which is significantly superior to that of the control probe MQP-Ac. Imaging studies on a mouse model of RA induced by λ-carrageenan show that MQP-Boc has excellent real-time and long-term imaging capabilities for RA. Besides, with MQP-Boc, significant increases in joint tissue viscosity were found during the RA process. All results indicate that MQP-Boc is an effective new tool for studying and diagnosing RA.