Background: Researches evaluating the influence of crown to implant ratios (c/i) on marginal bone level (MBL) and bone density changes of non-splinted single implants are still rare. The aim of this study was to assess the effect of c/i on MBL and density of peri-implant bone in non-splinted posterior implants. Methods: C/i, MBL and bone density changes were measured on standardized X-rays. The bone density changes were assessed according to the grey-scale values. Four interested areas (two at apical and two at middle of the peri-implant area) and two control areas were set to evaluate the grey-scale values of peri-implant bone. Radiographs at follow-up had been calibrated by control areas. Results: Seventy-three patients with a total of 117 non-splinted posterior implants were involved in this study, with a mean follow-up time of 36.23±10.40 months (24 to 72 months). The average anatomical c/i was 1.78±0.43, with a range of 0.93 to 3.06. The mean MBL change was 0.28±0.97mm, ranging between -2.75mm and 2.56mm. The correlation between c/i and MBL changes was without significant difference (r = -0.028, P = 0.766). The Pearson coefficient determined a significant correlation between gray-scale value changes and c/i, both at middle peri-implant areas (r = 0.301, P = 0.001) and at apical (r = 0.247, P = 0.009). Conclusions: Higher c/i of single non-splinted posterior implants was correlated with bone density increases at peri-implant areas, but not associated with MBL changes.