This study presents a novel approach to enhancing MIL-88B(Fe) for H₂S sensing by incorporating aniline trimer (ACAT). The successful synthesis and comprehensive characterization of ACAT, MIL-88B(Fe), and their composite, ACAT-MIL-88B(Fe), are detailed. The ACAT-MIL-88B(Fe) sensor demonstrates significantly superior performance, with a sensitivity increase to 643.5% at 9-10 ppm H₂S and a rapid response time of 288seconds. It maintains high sensitivity (450% response) even at 90% relative humidity and shows excellent selectivity for H₂S over other gases. Stability tests confirm over 600% responsiveness over 16 days. Density Functional Theory (DFT) calculations validate that H₂S adsorption is most stable at the Fe site of MIL-88B(Fe), with ACAT enhancing this interaction. This innovative sensor holds promise for highly sensitive, selective, and stable H₂S detection in industrial applications.