Quaternary AlInGaN alloy offers more degree of freedom in independently adjusting the band gap and lattice constant, and it shows the great potential in the fabrication of nitride optoelectronic and electronic devices. In this work, AlInGaN films were grown by metal-organic chemical vapor deposition and the p-type conduction was realized in compositionally graded quaternary AlInGaN. The element compositions in AlInGaN were confirmed by secondary ion mass spectrometry. The structural properties such as layer thickness, lattice polarity and surface morphology of the epilayers were characterized by cross-sectional scanning transmission electron microscopy and atomic force microscopy (AFM). The measured surface AFM images verify that the surface morphology of the quaternary AlInGaN film is smooth and it is free from V-shaped pits. Hall effect measurement results show that the grown graded AlInGaN is p-type with the hole concentration of ∼7.3 × 1016 cm−3 at room temperature. The realization of p-type conduction in AlInGaN can enrich the polarization engineering and the device structures of nitride semiconductors.