Objective To investigate the effects on ribbon synapse of inner hair cells by superpulsed CO2 laser-assisted cochleostomy in SD rats.Methods Eighteen SD rats were randomly divided into the laser-assisted surgery groups (2 W group and 5 W group),the sham-operated group and the control group.Ten of those were performed a cochleostomy using superpulsed CO2 laser with corresponding power.Auditory brainstem responses (ABR) were measured pre-and postoperatively.The ribbon synapses at apical and middle cochlear turns were observed under laser scanning confocal microscope and then were quantified with 3ds Max software.Results The postoperative ABR thresholds of the 2 W and 5 W groups were larger than the preoperative cases (t =-5.65,P ＜ 0.01 ; t =-4.97,P ＜ 0.01).The synapse numbers at the middle turn decreased significantly in the 5 W group (F =17.15,P ＜ 0.01),while no significant changes were noted at the apical turn(P ＞0.05).There was no statistical difference in the 2 W group(P ＞0.05).Conclusions The superpulsed CO2 laser-assisted cochleostomy with high-power is accompanied by synaptic injury,while no obvious effects by the low-power laser surgery,which might be the safe strategy to preform cochleostomy.