Aneuploidy including trisomy results in developmental disabilities and is the leading cause of miscarriages in humans. Unlike trisomy 21, pathogenic mechanisms of trisomy 18 remain unclear. Here, we successfully generated induced pluripotent stem cells (iPSCs) from human amniotic fluid cells (AFCs) with trisomy 18 pregnancies. We found that trisomy 18 iPSCs (18T-iPSCs) were prone to differentiate spontaneously. Intriguingly, 18T-iPSCs lost their extra 18 chromosomes and converted to diploid cells after 10 generations. fluorescence in situ hybridization analysis showed chromosome loss was a random event that might happen in any trisomic cells. Selection undifferentiated cells for passage accelerated the recovery of euploid cells. Overall, our findings indicate the genomic instability of trisomy 18 iPSCs bearing an extra chromosome 18.