Small aldehyde molecule are demonstrated to induce cationic diphenylalanine to assemble into monodisperse enzyme-responsive nanocarriers with high biocompatibility and excellent biodegradability. The formation of Schiff base covalent bond and accompanying pi-pi interaction of aromatic rings are found to be the mainly driving forces for the assembly of the nanocarriers. Interestingly, the nanocarriers show autofluorescence due to the n-pi* transitions of C = N bonds, which lends them visually traceable property in living cells. Importantly, the nanocarriers can be taken in by cells and biodegraded in the cells. In addition, doxorubicin is easily loaded into the nanocarriers with high encapsulation amount, and its release can be triggered by tyrisin under physiological conditions. Noticeably, even at a very low drug concentration, the doxorubicin-loaded nanocarriers still exhibit a much higher killing capacity of HeLa cells in vitro, compared to the equivalent-dose free doxorubicin, indicating they have a great potential biomedical application.