To examine the bonding of flowable resin composite restorations (F-restoration) to class 1 occlusal cavities with and without cyclic load stress, compared with that of a universal resin composite restoration (U-restoration). Two flowable composites and one universal composite (control) were applied with an adhesive system to 42 standardized class 1 occlusal cavities. The restored specimens were subjected to cyclic load stress and no stress modes. The microtensile bond strength (μ-TBS) of the dentin floor was measured. The U-restoration did not show pretesting failure. The F-restorations exhibited pretesting failure, regardless of the stress mode. The μ-TBS was not significantly different among the three restorations, regardless of the stress mode. The cyclic load stress did not influence the μ-TBS of the F-restorations; however, it significantly reduced μ-TBS in the U-restoration. The bonding reliability of the F-restorations was inferior to that of the U-restoration, for both stress modes.