We developed a method for rapid and precise determination of B isotope ratios by MC-ICP-MS through an optimization of washout method, mass-discrimination correction and chemical separation. Resultant reproducibility of δ11B values was ±0.4‰ (2 × SD) when a simple standard-sample bracketing technique was used, and it was improved to be better than ±0.2‰ by a mass discrimination correction with a 7Li/6Li isotopic reference. A mixed solution, which consists of HNO3- HF-mannitol, allowed a rapid washout of B memory in the sample introduction line. The validation of this technique to a wide range of δ11B value and various B signal intensities was confirmed from a series of B reference solutions with δ11B values of -20 to +40‰ and 25 to 125 ng/g B. Analyses of seawater standard (BCR-403) and carbonate standard (JCp-1) with sample sizes of less than 50 ng B gave δ11B values consistent with those determined by TIMS as Cs2BO2 +. The simple and high-precision technique developed here is applicable to various types of commercially supplied multiple collector ICP mass spectrometers without any modification of the sample introduction system from their original instrumental setting.