In this work, we report a one-step hydrothermal reaction to fabricate fluorescent carbon dots (CDs) using polyimide (PI) as precursor. The as-prepared CDs exhibit bright blue-green fluorescence and a favorable quantum yield of ca. 20%. Also, the fluorescent CDs show both pH dependence and an ion response towards metal ions, as well as a fluorescence shift after being passivated by various organic amines. In addition, the CDs can be used as fluorescent inks to achieve fluorescent patterns for promising applications in anticounterfeit and optoelectronic devices.