The ultimate goal of pediatric dentistry is to establish a strong adhesion to dental tissues, particularly with primary teeth, which tend to have weaker bond. This study aimed on assessing and comparing the microtensile bond strength in dentin restored with conventional composite (Filtek™ Z250), non-self adhering bulk-fill composite (SureFil™), or self-adhering bulk-fill composite (Surefil one™) in mandibular second primary molars. This study, was performed on 45 beams, obtained from (15) unidentified, freshly extracted mandibular second primary molars, that had been removed for reasons unrelated to this study (such as shedding). After the molars' dentin was exposed 1 mm under the dentin-enamel junction, they were randomly divided into three groups (n=5): FiltekTM Z250 group, SureFilTM group, and Surefil oneTM group. Then, molars were restored according to the restoration that was assigned to them. Every restored molar underwent 5000 cycles of thermocycling at a range of temperatures from 5 to 55°C, with 20s of dwell time and 10s of transfer time. The reconstructed molars were sectioned longitudinally in the buccolingual and mesio-distal directions to obtain 1mmx1mm beam thickness. The beams were subjected to tensile stress using a universal testing machine, and an analysis of the failure type was performed on each beam. Primarily, collected data was examined for outliers, following normality test (with a significance level of 0.05) by using Shapiro-Wilk and/or Kolmogorov-Smirnov tests. The current investigation found that the three groups' microtensile bond strength test showed a highly significant difference. The highest value was noted for SureFil™ group, followed by Filtek™ Z250 group, and then Surefil one™ group. The three tested groups did not differ significantly in their failure type analysis. The self-adhesive bulk-fill composite showed bond strength less than the acceptable minimal value that is needed to resist polymerization shrinkage stress for durable restoration.