MLO-A5 cells are a fully differentiated osteoblastic cell line with the ability to rapidly synthesise mineralised extracellular matrix (ECM). We used MLO-A5 cells to develop a system for studying the mechanical modulation of bone matrix formation in 3D using a cyclic compressive loading stimulus. Polyurethane (PU) open cell foam scaffolds were seeded with MLO-A5 cells under static conditions and loaded in compression at 1 Hz, 5% strain in a sterile fluid-filled chamber. Loading was applied for only 2 h per day on days 5, 10 and 15 of culture and cell-seeded scaffolds were assayed on days 10, 15 and 20 of culture. Collagen content as assayed by Sirius red was significantly (2 fold) higher at days 15 and 20 in loaded samples compared with static controls. Calcium content as assayed by alizarin red was significantly (4 fold) higher by day 20. The number of viable cells as assayed by MTS was higher in loaded samples at day 10 but there was no difference by days 15 and 20. Loaded samples also had higher stiffness in compression by the end of the experiment. The mRNA expression of type I collagen, osteopontin and osteocalcin was higher, after a single bout of loading, in loaded than in non-loaded samples as assayed by RT-PCR. In conclusion, mineralisation by fully differentiated osteoblasts, MLO-A5s, was shown to be highly sensitive to mechanical loading, with short bouts of mechanical loading having a strong effect on mineralised matrix production. The 3D system developed will be useful for systematic investigation of the modulators of in vitro matrix mineralisation by osteoblasts in mechanobiology and tissue engineering studies.