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The creation of 3D THz photonic crystals with tunable THz properties in real time under proper external stimuli could endow them with novel functions for cutting-edge THz technology applications. However, to tune THz properties by structure variation under external stimuli largely limits their potential to be integrated with other components to form THz devices. In this work, a composite ink composed of VO2 nanoparticles and polydimethylsiloxane (PDMS) is developed with proper rheological properties for direct-writing to create 3D THz photonic crystals with thermally tunable THz properties without the need of structure variation. Due to the reversible insulator-metal phase transition of VO2 nanoparticles under proper thermal stimulus, thermally tunable refractive indices are observed for the VO2/PDMS composite ink, which results in interesting thermally tunable THz properties for 3D VO2/PDMS THz photonic crystals without changing their structure. This work opens up an unexplored avenue to create “smart” 3D THz photonic crystals responsive to external thermal stimulus by direct-writing technology, which eliminates the need of structure variation to tune their THz properties and paves the way for their integration into THz devices to create novel functions for cutting-edge THz technology.