Acetylcholinesterase (AChE) activity and its inhibitor assays play a vital role in the early diagnosis and drug screening of certain diseases. In this work, we for the first time found that the protein-inorganic hybrid nanoflowers (HNFs) [BSA-Cu₃(PO₄)₂] exhibits an obvious laccase-like catalytic activity. Further, through the regulation of laccase-mimicking activity, we developed a convenient and original colorimetric tactic for sensitive and selective assaying of acetylcholinesterase (AChE) activity and its inhibitors. Most surprisingly, AChE can catalyze acetylthiocholine (ATCh) into thiocholine (TCh), which could significantly enhance the catalytic activity of BSA-Cu₃(PO₄)₂ HNFs. The enhanced laccase-like activity accelerates the chromogenic reaction between 2,4-dichlorophenol (2,4-DP) and 4-aminoantipyrine (4-AP), and the relevant product exhibits a red color which is owing to the reduction of Cu²⁺ in the HNFs to Cu⁺ by TCh. According to the facile signal-on response with clear response mechanism, our method has been successfully applied for the highly sensitive detection of AChE activity with a linear range of 0.25–5 mU/mL, and testing AChE inhibitors, especially obtaining satisfactory results in real samples. It is expected that such facile strategy could pave the way for the potential applications of biometric catalysts in disease diagnosis and environmental monitoring.