A major component of Alzheimer's disease pathology is the accumulation of amyloid-β (Aβ), a peptide that is known to weaken synaptic transmission. Whereas both AMPA receptor (AMPAR) and NMDA receptor (NMDAR) currents are affected by Aβ oligomers, not all synapses are equally vulnerable to the toxic effects of Aβ. We set out to elucidate the roles of the different AMPAR and NMDAR subunits in synapse susceptibility to Aβ. Whole-cell patch clamp recordings were performed in hippocampal CA1 neurons that overexpress Aβ oligomers. Variance analysis was used to disentangle whether this decreased synaptic transmission is a consequence of weakening and/or loss of synapses. We found that AMPAR subunit composition determines which synapses are vulnerable to Aβ. Specifically, synapses lacking the GluA3 AMPAR subunit, and thus only containing GluA1 AMPARs, were resistant to Aβ-induced depression of postsynaptic AMPA currents and to the loss of synapses. Thus, the presence of GluA3 makes synapses vulnerable to Aβ. The fate of these susceptible GluA3-containing synapses is then determined by NMDAR subunit composition. These susceptible synapses are either completely removed (i.e., both AMPAR and NMDAR currents are lost) or they show decreased AMPAR but not NMDAR currents. Those synapses that are lost are the ones that contain NMDAR subunit GluN2B, but interestingly this is dependent on the presence of the GluN2A subunit. In conclusion, AMPAR subunit composition determines whether synapses are susceptible or resistant to the detrimental effects of Aβ, while NMDAR subunit composition determines whether susceptible synapses are weakened or lost entirely.