Because palladium is widely used in various catalysts and converters, which results in a high level of contamination of water systems and the soil by residual palladium, there is an urgent need for Pd2+‐sensitive and ‐selective probes. Based on the special affinity of Pd2+ to conjugated double‐bond ligands, two fluorescence probes (RPd2 and RPd3) that contain conjugated allylidene‐hydrazone ligands that link to colorless rhodamine‐spirolactam have been developed. The results show that conjugated allylidene‐hydrazones have a much better affinity toward Pd2+, and consequently provide the probes with more acute color change and fluorescence enhancement (≈170‐fold), and better selectivity over other metal ions (especially platinum‐group elements, or PGEs) than the unconjugated allyl‐hydrazine. With richer electron density and a more suitable stereo effect in the allylidene‐hydrazone group, RPd2 displays the best specificity toward Pd2+ and affords convenient detection by the naked eye. Its potential application for Pd2+‐contaminated water and soil‐sample analysis is revealed by proof‐of‐concept experiments.