High precision SIMS Al-26-Mg-26 isotopic analyses were performed in order to detect the excesses of (26)mg that derived from in situ decay of Al-26 (half-life of 0.73 million years) in primitive meteorites. The electron multiplier is used to analyze Mg isotopes in Al-rich glass using 5 mum O-2(-) primary ion beam. The EM dead time correction and Al/Mg sensitivity calibration are applied to obtain accurate data. The precisions of Mg-26/Mg-24 isotopic ratios and Al-27/Mg-24 atomic ratios were 2-5parts per thousand and 10%, respectively. The relative formation time of less than I million years among chondrules is able to be determined. Further attempt was made to improve the precision of Mg isotopic ratios using the multi-collector Faraday cups. The preliminary tests showed both internal and external precisions of better than 0.1parts per thousand. (C) 2002 Elsevier Science B.V. All rights reserved.