We measure both nonlinear absorption and nonlinear refraction in a C H 3 N H 3 P b B r 3 single crystal using the Z-scan technique with femtosecond laser pulses. At 1000 nm, we obtain values of 5.2 cm/GW and + 9.5 ⋅ 10 − 14 c m 2 / W for nonlinear absorption and nonlinear refraction, respectively. The sign and magnitude of the observed refractive nonlinearity are reproduced well by the two-band model. Our results suggest that the large nonlinear refractive index measured in perovskite nanostructures cannot be explained by an intrinsically high bound-electronic nonlinear refractive index in this emerging material class but is possibly caused by free carriers or quantum confinement effects.