A wet paper friction material, mainly used for a slip lock-up of an automatic transmission, obtained by impregnating a paper material with a thermosetting resin, thermosetting, and molding under pressure, to attain compatibility between a good frictional characteristic and good fatigue strength under compression, wherein the paper material, in addition to a cellulose pulp and a filler, contains 30 to 80 wt % of aramid pulp with its drainability being adjusted to 250 to 440 ml in a total amount of pulp, and further contains, as a friction modifier, diatomaceous earth cylindrically formed so as to be net-like in the cylinder part and having its mean length 4 to 6 .mu.m.