The recent advances in understanding the borate autocausticizing process indicate that partial substitution of calcium oxide with borate could be a very attractive and economical way to reduce the energy cost in time kilns in kraft mill operations. Accurate and timely analysis of sulfide, hydroxide, and carbonate concentrations in recausticizing process liquors is essential to the successful mill trials of borate autocausticizing. Unfortunately, the traditional ABC titration method fails in analyzing the hydroxide, sulfide, and carbonate concentration due to the presence of borate. This paper demonstrates an ATR-UV spectroscopic sensor for rapid and simultaneous determination of sulfide, hydroxide, and carbonate in kraft liquors that contain borate. The results of on-site mill trials showed good agreements between the ATR-UV method and the ABC titration method combined with the atomic absorption method. The ATR-UV technique is rapid, simple. and can be used for on-line process control.