PURPOSE: An adjustor for drilling mud, obtained by reacting sodium humate, etc. with sodium acrylate, etc. at a specific ratio in the presence of a radical polymerization initiator, containing no harmful heavy metal, e.g. Cr, having improved dispersibility, salt resistance and heat-resistance stability, and useful for oil wells, etc.

CONSTITUTION: A adjustor obtained by reacting (A) 100pts.wt. sodium or potassium humate with (B) 30W300pts.wt. sodium or potassium acrylate in the presence of a water-soluble radical polymerization initiator, e.g. hydrogen peroxide or ammonium persulfate, in an aqueous solution preferably at 50W100°C for 30minW4hr by adjusting the concentration of the reactants to usually 10W40wt% in the reaction and the pH of the aqueous reaction solution to usually 5W10. The aqueous solution of the above-mentioned reaction product may be directly used as the mud adjustor, but usually is granulated or powdered by drying for use.