All-inkjet-printed organic thin-film transistors take advantage of low-cost fabrication and high compatibility to large-area manufacturing, making them potential candidates for flexible, wearable electronics. However, in real-world applications, device instability is an obstacle, and thus, understanding the factors that cause instability becomes compelling. In this work, all-inkjet-printed low-voltage organic thin-film transistors were fabricated and their stability was investigated. The devices demonstrate low operating voltage (<3 V), small subthreshold slope (128 mV/decade), good mobility (0.1 cm2 V−1 s−1), close-to-zero threshold voltage (−0.16 V), and high on/off ratio (>105). Several aspects of stability were investigated, including mechanical bending, shelf life, and bias stress. Based on these tests, we find that water molecule polarization in dielectrics is the main factor causing instability. Our study suggests use of a printable water-resistant dielectric for stability enhancement for the future development of all-inkjet-printed organic thin-film transistors.