Flax fibers are often used in reinforced composites which have exhibited numerous advantages such as high mechanical properties, low density and biodegradablility. On the other hand, the hydrophilic nature of flax fiber is a major problem. In this study, we prepare the soybean oil based composites reinforced with protein coated and lipid acylated flax fibers and compare their water uptake properties. Results showed that water resistance properties of the composites are improved where treated flax fibers are used. The composite with lipid acylation of the flax fiber exhibited to enhance tensile strength and water resistance properties. Influences of fiber length, fiber loading and pressure on mechanical properties are also reported.