The effect of interface on the mechanical properties of glass fibre/phenolic composites is discussed in this paper. Standard and silane modified resins are used as matrix, and a yam and two kinds of rovings with different sizing are used as reinforcement. The effect of fibre on wetting is evaluated, and it is shown that sizing specially developed for phenolic resin is quite effective to improve resin impregnation into the fibre bundle. The mechanical properties are evaluated by using the resin impregnated unidirectional fibre bundle composite specimens. The effects of resin and fibre on strength and crack propagation are evaluated by the lateral compression test. The type of the fibre affected the dispersion of fibres in the matrix resin, and the roving developed for phenolic resin gave the best dispersion of the fibre. This led the high mechanical properties and high resistance to the crack initiation.