Human polypyrimidine tract-binding protein PTB is a multifunctional RNA-binding protein with four RNA recognition motifs (RRM1 to RRM4). PTB is a nucleocytoplasmic shuttle protein that functions as a key regulator of alternative pre-mRNA splicing in the nucleoplasm and promotes internal ribosome entry site-mediated translation initiation of viral and cellular mRNAs in the cytoplasm. Here, we demonstrate that PTB and its paralogs, nPTB and ROD1, specifically interact with mitochondrial (mt) tRNA Thr both in human and mouse cells. In vivo and in vitro RNAbinding experiments demonstrate that PTB forms a direct interaction with the T-loop and the D-stem-loop of mt tRNA Thr using its N-terminal RRM1 and RRM2 motifs. RNA sequencing and cell fractionation experiments show that PTB associates with correctly processed and internally modified, mature mt tRNA Thr in the cytoplasm outside of mitochondria. Consistent with this, PTB activity is not required for mt tRNA Thr biogenesis or for correct mitochondrial protein synthesis. PTB association with mt tRNA Thr is largely increased upon induction of apoptosis, arguing for a potential role of the mt tRNA Thr /PTB complex in apoptosis. Our results lend strong support to the recently emerging conception that human mt tRNAs can participate in novel cytoplasmic processes independent from mitochondrial protein synthesis.