Ti-Si-N nanocomposite films were deposited by multitarget reactive magnetron sputtering. Energy dispersive spectroscopy, X-ray diffraction, transmission electron microscopy, and x-ray photoelectron spectroscopy were employed to characterize their microstructure and a microhardness tester was used to measure their hardness. The influence of substrate temperature on these films was investigated, too. The results reveal that the films consist of TiN and Si3N4. Si3N4 exists as amorphous, which strongly prevents the growth of TiN grains and causes TiN to form a nanocrystalline or amorphous phase. The hardness of films deposited at room temperature reaches the peak value of 36 GPa at a Si content of 4.14 at. %, and then decreases gradually with the increase of Si content. The enhancement of the substrate temperature weakens the restraint effect of amorphous Si3N4 on the growth of TiN grains, which results in coarse TiN grains and subsequently leads to a lower peak value and a slower decrease of the hardness of the films.