The stability of Δ⁹-tetrahydrocannabinol acetate (Δ⁹-THC-OAc) in the presence of diluents or during vaping was investigated. Laboratory-made pure Δ⁹-THC-OAc and glycerol, propylene glycol (PG), or polyethylene glycol 400 (PEG400) were dissolved in ethanol and subjected to the quantification method for Δ⁹-tetrahydrocannabinol (Δ⁹-THC) recommended by UNODC. The pure Δ⁹-THC-OAc diluted by glycerol, PG, or PEG400 was stored at 40°C for 27 days. A retail liquid product of Δ⁹-THC-OAc containing Δ⁹-THC as an impurity was stored at 80°C for 28 days in the presence of glycerol, PG, or PEG400. A cartridge containing the Δ⁹-THC-OAc liquid was installed in an e-cigarette device, which was heated and vaporized using a syringe connected to the cartridge through a silicone tube. The Δ⁹-THC-OAc liquid was put into a test tube and heated at 200 or 400°C for 5 min. The relative concentrations of cannabinoids in the test solution before and after each operation were measured by liquid chromatography with photodiode array detection or by gas chromatography with flame ionization detection. Δ⁹-THC was not detected in any cases of pure Δ⁹-THC-OAc, and it decreased or disappeared in all cases of Δ⁹-THC-OAc liquid. The present result showed that Δ⁹-THC-OAc does not decompose into Δ⁹-THC during each process.