Macro-defect free (MDF) cement is a cement-polymer composite with superior flexural strength although produced by mixing cement with small amounts of polymer and water. Special production technique and the crosslinking occurred between cement and polymer are important factors for obtaining such high strengths. However, MDFs lose considerable strength when exposed to water. The objective of this study was to explore the effects of TiO2 addition on flexural strength and water sensitivity of MDF. In this study, MDF cements were produced by adding up to 4% TiO2 by weight of cement. Biaxial flexural test as well as Atomic Force Microscopy (AFM) and Fourier Transform Infrared Spectroscopy (FTIR) tests were conducted in order to investigate the effect of TiO2 addition. TiO2 addition improved the water resistance of MDF cements in some batches, especially with 2% addition possibly due to the C-PVA-O-Ti-O-C-PVA bond and this cross-linking mechanism together with C-PVA-O-Al-O-C-PVA bonds cause a more stable polymer network.