Only mannitol or glycerine is generally used for the determination of boric acid in a nickel plating solution in order to make its acidic property so strong that it can be titrated with NaOH. However, these solutions give very ambiguous color change of indicator due to the precipitation of nickel salts. Therefore, only experienced chemists or well trained workmen can accurately confirm the actual end point of the titration. For eliminating such interference of nickel salts and easily confirming the end point by any persons, the author attempted to find out a solution which produces no precipitates during the titration in these experiments; and also, he tried to furnish the reason for ambiguousness in titration.The following results were obtained after many experiments.(1) In any titrations which produce nickel salts such as Ni(OH)2, the salt is formed until very approximate to the end point, which shows some error by the consumption of titrant (NaOH). Then, the pink color of phenolphthalein is absorbed by Ni(OH)2 and the pH jumping at the end point is also diminished to as little as less than 15% of the total phenolphthalein pH range.(2) Known methods by complex salts of citrate, which do not produce precipitates of Ni(OH)2, are also not very satisfactory; because, the pH jumping at the end point is only about 35% and the color change of phenolphthalein is from blue-green to purple-red.(3) New methods by complex salts of oxalate were attempted in these experiments. They also did not produce precipitates of Ni(OH)2 and were very satisfactory in color change at the end point; because, the pH jumping at the end point was about 65% and the color change was from blue-gree to purple-red. In these methods, analytical cost was minimized by the use of less amounts of cheaper chemicals than the conventional citrate complex methods. The mixture of chemicals used was composed of 37g/l if sodium oxalate (Na2C2O4·5H2O), 2g/l of phenolphthalein, and 400ml/l of glycerin. The accuracy of analysis was within the error of 0.5%.(4) The procedure of analysis was as follows. One ml of nickel plating solution was taken out and to it were added 20ml of water and 20ml of the above mixture for the indicator. The solution was titrated with 0.1N NaOH. The quantity of boric acid was calculated by the following equation.Boric acid (g/l)=6.184×F×ml