Objective To explore the effects of saline instillation on sputum and cardiopulmonary functions of neonates with mechanical ventilation when endotracheal suctioning.Methods Totals of 20 neonates with mechanical ventilation were recruited.Saline instillation was implemented before endotracheal suction at different doses and concentrations.Sputum and cardiopulmonary parameters were recorded after saline instillation and 1 minute,2 minutes,10 minutes after suctioning,including SpO2,PIP,HR,SBP and DBP.Results The 0.5 ml saline instillation group has more sputum than that of no saline instillation group,and the difference was statistically significant [ ( 1.27 ± 0.77 ) ml vs (0.74 ± 0.55 ) ml; P =0.006 ],while no significant difference was found between 0.5 ml saline instillation group and 1.0 ml saline instillation group [ ( 1.27 ±0.77) ml vs (0.99 ± 0.66 ) ml; P =0.072 ].There was no significant effect of the different dose and concentration of saline instillation on sputum of the neonates ( P ＞ 0.05) and on the cardiopulmonary parameters (P＞0.05).SpO2,HR and SBP were significantly changed with time (F =41.567,39.088,6.715,respectively ;P ＜ 0.05 ).SpO2 in the points of 2 minute and 10 minute after suctioning were higher than that in the points of saline instillation and 1 minute after suction; HR in the points of 1 minute and 2 minute after suctioning were higher than that in the point of saline instillation; SBP in the points of 1 minute and 2 minute after suctioning were higher than that in the points of saline instillation and 1 minute after suction.PIP and DBP were not significantly changed with time ( P ＞ 0.05 ).Conclusions Instillation of 0.5 ml normal saline in neonates with mechanical ventilation when endotracheal suctioning may increase sputum and have little side effects on cardiopulmonary function.