To increase paper strength, refining and wet pressing are performed. Many researches were carried out to identify the origin of paper strength. Since fracture toughness was governed by stress concentration, fracture toughness reflects microscopic paper strength. The aim of this paper is to analyze how paper strength was affected by changes of refining and wet-pressing. Fiber properties and structural, tensile and fracture properties of hand­sheets were evaluated. Especially, fracture toughness was evaluated by J-integral. As the refining proceeds, stock properties maybe divided into two stages such as fibers activation and fines activation according to freeness. In fibers activation stages, about 750-450 mL CSF, the fracture toughness increased with refining and wet pressing but in fines activation stages, about 450-250 mL CSF, the fracture toughness increased only with wet pressing. It is clear that fracture toughness was affected not only by fibers properties but also by fines properties in fines activation stages.