Objective: We aimed to investigate the effectiveness of the liquid PRF-DBBM mixture on new bone formation in maxillary sinus augmentation. Material and Methods: Seven patients requiring two-stage bilateral maxillary sinus augmentation were included in the study. The patients were selected according to the criteria of having an alveolar bone height of at least 2 mm in the atrophic region. The elevated sinus cavities were randomly grafted with DBBM + liquid PRF (test) or DBBM alone (control) in a split-mouth design. Bone samples were collected during implant surgery with a trephine bur for histomorphometric evaluation after 4 months. Results: In the control group, the newly formed bone was 39.49%, the mature bone was 15.66%, the residual graft was 15.62%, and the fibrous tissue ratio 28.59%, while in the test group, the newly formed bone (NFB) was 45.95%, the mature bone was 14.40%, the residual graft was 10.32%, and the fibrous tissue was 29.31%. No statistically significant difference was found between the groups in terms of the parameters studied (p > 0.05). The mean osteocalcin score in the control group was 2.70 ± 0.39, while it was 2.81 ± 0.36 in the test group. There was no statistically significant difference between the averages of osteocalcin scores of the groups (p > 0.05). Conclusion: The results of our study showed that DBBM is a reliable graft material for maxillary sinus augmentation even in the early period. Combining of DBBM with liquid-PRF contributed to new bone formation over a four-month period, but this contribution was not statistically significant.