To provide a curlproof paper prevented from curling after subjected to thermal transfer printing by the use of an electrophotographic copier or the like, and to provide a method for producing the curlproof paper.

This curlproof paper is characterized by being ±0.5 wt.% in the difference between the obverse and reverse ash contents (heereafter, referred to as obverse/reverse ash content difference) and 0.63-0.70 mm in the fiber length of a pulp suspension issued from a headbox (hereafter, referred to as slice flow). The other objective method for producing the curlproof paper is also provided.