In this study, we employed tannic acid (TA)-functionalized silver nanoparticles (TA@AgNPs) as colorimetric probe for the simultaneous and sensitive detection of Al(III) and F ions. The proposed sensor was based on the aggregation and anti-aggregation effects of target Al(III) and F ions on TA@AgNPs, respectively. Because of the strong coordination bond between Al(III) ions and TA, the addition of Al(III) ions to TA@AgNPs could cause aggregation and, hence, result in a significant change in the absorption and color of the test solution. Interestingly, in the presence of F ions, the aggregation effect of Al(III) ions on TA@AgNPs can be effectively prevented. The extent of aggregation and anti-aggregation effects was concentration-dependent and can be used for the quantitative detection of Al(III) and F ions. The as-proposed sensor presented the sensitive detection of Al(III) and F ions with limits of detection (LOD) of 0.2 and 0.19 μM, respectively. In addition, the proposed sensor showed excellent applicability for the detection of Al(III) and F ions in real water samples. Moreover, the sensing strategy offered a simple, rapid, and sensitive detection procedure and could be used as a potential alternative to conventional methods, which usually involve sophisticated instruments, complicated processes, and a long detection time.