The effects of different post-space pretreatments on the retentive force of fiber posts cemented with a self-adhesive resin cement were investigated.Twenty-eight single-canal premolars were obturated by Resilon using warm vertical compaction and treated with distilled water,2.5% NaOCl,17% EDTA and 2.5% NaOCl;or 17% EDTA,2.5% NaOCl,and ultrasonic agitation(U/E/N treatment).Subsequently,radicular dentin surfaces were observed under scanning electron microscopy(SEM).RelyX Fiber Posts were cemented in the treated canals by using RelyX U100,and thin-slice push-out test and SEM observation of coronal and apical regions of the specimens were performed.Data were analyzed using two-way ANOVA and Tukey's HSD posthoc tests,and the percentage of failure type was calculated.Ultrasonic/EDTA/NaOCl irrigation showed the maximum effectiveness in removing the smear layer and debris on the dentin surface.The apical bond strength of the experimental groups was significantly higher than that of the control group(P< 0.05).Adhesive failure between cement and dentin was the most common mode of failure.No obvious RDIZ or resin tag was detected.Chemical irrigants facilitated the bonding of these fiber posts,and ultrasonic activation improved retention.Future studies should evaluate the effectiveness of irrigation on fiber post push-out strength in fatigue cycling condition. The effects of different post-space pretreatments on the retentive force of fiber posts cemented with a self-adhesive resin cement were investigated. Twenty-eight single-canal premolars were obturated by Resilon using warm vertical compaction and treated with distilled water, 2.5% NaOCl , 17% EDTA and 2.5% NaOCl; or 17% EDTA, 2.5% NaOCl, and ultrasonic agitation (U / E / N treatment) in the treated canals by using RelyX U100, and thin-slice push-out test and SEM observations of coronal and apical regions of the specimens were performed. Data were analyzed using two-way ANOVA and Tukey's HSD posthoc tests, and the percentage of failure type was calculated. Ultrasonic / EDTA / NaOCl irrigation showed the maximum effectiveness in removing the smear layer and debris on the dentin surface. apical bond strength of the experimental groups was significantly higher than that of the control group (P <0.05) .Adhesive failure between cement and dentin was the most common mode of failure. No obvious RDIZ or resin tag was detected. Chemical irrigants facilitated the bonding of these fiber posts, and ultrasonic activation improved retention. Future studies should evaluate the effectiveness of irrigation on fiber post push-out strength in fatigue cycling condition.