The present invention provides a method for preparing cell extract for high-performance cell-free protein synthesis reactions, comprising the elimination of low molecular weight substances that have protein synthesis inhibitory activity, from cell extracts that have cell-free protein synthesis activity, by such methods as dialysis, gel filtration and ultrafiltration. Also provided is a ready-made cell-extract for cell-free protein synthesis employing this method. Furthermore, the formation of insoluble matter can be reduced by performing the process for eliminating the low molecular weight substances that inhibit protein synthesis in the co-presence of ATP, GTP or amino acids, so as to stabilize the cell extract.