Acoustic emission (AE) accompanied by the intergranular fracture was examined in Al-Mg-Si base alloys. In as-quenched specimens, a peak of AE event counts was observed only at a yield point and then it reduced with increment in plastic strain. On the other hand, in a T6-aged specimen, the peak of AE event counts appeared not only at the yield point but also at the moment of intergranular fracture. The AE signals associated with the intergranular fracture had its amplitude ranges up to 100dB. The increase in AE amplitude revealed that a high AE energy was emitted from the specimen when the intergranular fracture occurred. Similar results on the increase in AE amplitude was also obtained when a T4-tempered Al-Mg-Si alloy aged at 175degreesC for 0.5h was tensile tested at a slow strain rate of -10(-6)s(-1) at room temperature.