The cubic optical nonlinearity of molybdenum disulfide (MoS₂) nanoflakes was characterized by Z-scan and I-scan with resonant excitation. The excitation source was a ~6 ns laser at 532 nm with a 10 Hz repetition rate. The open and closed Z-scan analyzed the nonlinear absorption and nonlinear refraction properties of MoS₂ nanoflakes. The I-scan technique characterized the nonlinear transmittance properties of MoS₂ nanoflakes at the peak and valley of closed Z-scan trace as a function of excitation intensity.