We report out experimental results on Z-scan characteristics of co-existence of Kerr effects and transient thermo-optical effects in Kerr media in the nanosecond regime.The transition of peak-valley pattern under a certain condition was observed.There is a basic agreement between experimental data and numerical modeling.Meanwhile, a new single peak pattern or platform pattern of Z-scan curves was observed while the transient thermally induced optical nonlinearity counterbalances with Kerr effects.The research is significant to analyze correctly Z-scan measurements using a nanosecond pulse laser.