The aim of this histomorphometric study was to assess the bone regeneration potential of beta-tricalcium phosphate with fibronectin (β-TCP-Fn) in critical-sized defects (CSDs) in rats calvarial, to know whether Fn improves the new bone formation in a short time scope.  CSDs were created in 30 Sprague Dawley rats, and divided into four groups (2 or 6 weeks of healing) and type of filling β-TCP-Fn, β-TCP, empty control). Variables studied were augmented area (AA), gained tissue (GT), mineralized/non mineralized bone matrix (MBM/NMT) and bone substitute (BS). 60 samples at 2 and six weeks were evaluated. AA was higher for treatment groups comparing to controls (p < 0.001) and significant decrease in BS area in the β-TCP-Fn group from 2 to 6 weeks (p = 0.031). GT was higher in the β-TCP-Fn group than in the controls expressed in % (p = 0.028) and in mm2 (p = 0.011), specially at two weeks (p=0.056).  Both β-TCP biomaterials are effective as compared with bone defects left empty in maintaining the volume. GT in defects regeneration filed with β-TCP-Fn are significantly better in short healing time when comparing with controls but not for β-TCP used alone in rats calvarial CSDs.