Polymeric nanoparticles, capable of encapsulating imaging agents and therapeutic drugs, have significant advantages for simultaneous diagnosis and therapy. Nonetheless, improvements in the loading contents of the active agents are needed to achieve enhanced imaging and effective therapeutic outcomes. Aiming to make these improvements, a hydrotropic micelle (HM) was explored to encapsulate superparamagnetic iron oxide nanoparticles (SPIONs) as the magnetic resonance (MR) imaging agent and paclitaxel (PTX) as the hydrophobic anticancer drug. Owing to its hydrotropic inner core with hydrophobic nature, HM could effectively encapsulate both of PTX and SPION via the simple dialysis method. The hydrodynamic size of HM increased from 68 to 178nm after physical encapsulation of SPION and PTX. Transmission electron microscopy analysis of HM bearing SPION and PTX (HM-SPION-PTX) revealed a spherical morphology with SPION clusters in the micelle cores. The micelles released PTX in a sustained manner. The bare HM and HM-SPION showed no toxicity to SCC7 cells, whereas HM-PTX and HM-SPION-PTX showed dose-dependent cytotoxicity that was lower than free PTX. HM-SPION-PTX exhibited 8.1-fold higher T(2) relaxivity than HM-SPION, implying potential of HM-SPION-PTX as the contrast agent for MR imaging. When systemically administered to tumor-bearing mice, HM-SPION-PTX was effectively accumulated at the tumor site, allowing its detection using MR imaging and effective therapy. Overall, these results suggested that HM-SPION-PTX is a promising candidate for combined diagnosis and treatment of cancer.