AIM To investigate the effect of MPP+ on the midbrain neurons of SAMP8 mouse in vitro, which provide the cell model for PD study. METHODS SAMP8 mouse primary midbrain cell cultures were obtained from mice within 1 day after birth. On the sixth day after culturing, the cultures were treated with 100 micromol/L of MPP+ for 6 hours, 9 hours, 12 hours and 24 hours, then the cells were fixed and followed by immunofluorescence or Western blot analysis for the expressed location and the level of TH respectively. RESULTS MPP+ led to the morphological changes of primary cultured midbrain neurons of SAMP8 mouse. The neurons had intact morphous with strong immunoreactivity, many and long dendrites in control group. Compared with the control group, the neurons had fewer and thinness dendrites with weak immunoreactivity in MPP+ group. MPP+ significantly decreased midbrain neurons numbers with marked decrease of TH protein levels after its treatment for 9 h. CONCLUSION MPP+ had neurotoxicity effect on primary cultured midbrain neurons of SAMP8 mouse. Since MPP+ led to marked decrease of neuronal numbers and TH protein levels, it is suggested that MPP+ can cause the DA neuronal degeneration in primary midbrain cell cultures.