The aim of this in vivo microcomputed tomographic (μCT) study was to compare the efficacy of Mucograft (MG) vs resorbable collagen membranes (RCMs) in facilitating guided bone regeneration (GBR) around standardized calvarial defects in rats. Forty female Wistar albino rats with a mean age and weight of 6 to 9 weeks and 250 to 300 g, respectively, were used. With the rats under general anesthesia, the skin over the calvaria was exposed using a full-thickness flap. A standardized calvarial defect with a 4.6-mm diameter was created in the left parietal bone. For treatment, the rats were randomly divided into four groups (n = 10 per group): (1) defects covered with MG (MG group); (2) defects covered with an RCM (RCM group); (3) defects filled with xenograft bone particles and covered by MG (MG + bone group); and (4) defects filled with xenograft bone particles and covered by an RCM (RCM + bone group). Primary closure was achieved using interrupted resorbable sutures. The animals underwent high-resolution, three-dimensional μCT scans at baseline and at 2, 4, 6, and 8 weeks after the surgical procedures. Data regarding volume and bone mineral density (BMD) of newly formed bone (NFB) and bone particles revealed an increase in the volume of NFB in all the groups from baseline to 8 weeks. The MG group had the lowest volume of NFB (mean ± standard deviation [SD], 1.32 ± 0.22 mm3). No significant differences in mean ± SD values for volume of NFB were observed between the RCM (3.50 ± 0.24 mm3) and MG + bone (3.87 ± 0.36 mm3) groups, but their values were significantly lower than that of the RCM + bone group (2.95 ± 0.15 mm3, F = 131.91, dfN = 2, dfD = 27, P .001). Significant differences in BMD of NFB between the groups (F = 332.46, dfN = 3, dfD = 36, P .001) and during different data collection periods (F = 97.04, dfN = 3, dfD = 36, P .01) were observed, with the RCM group having the highest mean ± SD BMD of NFB (0.42 ± 0.05 g/mm3). Significant differences in the bone particle volume between the RCM + bone and MG + bone groups (F = 91.04, dfN = 1, dfD = 18, P .05) and at different data collection periods (F = 314.12, P .01) were observed, with the RCM + bone group displaying greater reduction in both volume (36.8%) and BMD (19.7%) of bone particles. The present in vivo μCT study demonstrated that RCM is better than MG in enhancing new bone formation in rat calvarial standardized defects when used in combination with mineralized particulate graft material.