This study was conducted to evaluate the physical and chemical properties of Scots pine (Pinus sylvestris L.) sapwood modified with tannin-based formulas. Wood samples were pressure impregnated with tannin solution at five different concentrations of citric acid (0, 2, 10, 20, and 40 wt/wt%). The tannin-modified samples were analyzed by mean of their weight percentage gain (WPG), leaching resistance (LR), bulking coefficient (BC), anti-swelling efficiency (ASE), Fourier-Transform Infrared (FTIR) spectroscopy, and optical microscopy, and the results were compared with unmodified sapwood and heartwood samples. It is observed that the WPG and dimensional stability of the samples increased with increasing the citric acid (CA) concentrations and the highest WPG was attained (44%) with a formulation containing 20% CA while, the BC, LR, and ASE values were considerably higher in the samples modified with 40% CA concentration as compared to other modification formulas and also the unmodified sapwood and heartwood samples. FTIR spectroscopy analyses showed higher esterification degree with higher concentrations of CA. Overall, this study suggests the potential of a fully bio-based tannin formula to improve the water-related properties of Scots pine sapwood.