PURPOSE: To obtain a titled recording paper of high color developing recording density and good dot reproducibility, by specifying the fiber length distribution of a paper substrate.

CONSTITUTION: A thermal color developing layer is provided on a paper substrate consisting of a base paper wherein the fiber length distribution measured by screening method (JIS-P-8207) is 10% on under in 24-mesh retention wt% as well as 60wt% or under in the total of 24-mesh retention wt% and 42-mesh retention wt%. LBSP, LBKP, and NDP are preferably used as a pulp to obtain aforesaid fiber length distribution because they can easily be processed into short fibers. On the other hand, the desired fiber distribution can be obtained by controlling the type of beating machine, beating density, beating load, and the like. Additionally, it is preferably that 10wt% or over of pigment is contained in pulp. Accordingly, the thermal recording paper having sperior characteristics in color developing recording density as well as dot reproducibility can be obtained.