Alzheimer's disease (AD) is a common chronic neurodegenerative disease that manifests as cognitive impairment and behavioral deficits and severely threatens the health of the elderly. Acetylcholinesterase (AChE) plays a vital role in biological signaling and is an essential target for the early diagnosis and treatment of AD. Herein, 2D Zn-TCPP(Fe) nanosheets (NSs) employing Zn2+ and Fe-bound tetrakis(4-carboxyphenyl)porphyrin ligands were prepared through a surfactant-assisted synthetic method. The ultrathin two-dimensional (2D) metal-organic framework structures exhibited high peroxidase-like activity, which allowed the catalysis of the H2O2-initiated oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB (ox-TMB). Such catalytic performance inspired us to develop a convenient, rapid, and sensitive acetylcholinesterase activity assay, during which AChE can catalyze the substrate acetylthiocholine (ATCh) to produce thiocholine (TCh), and TCh could especially enable the degradation of 2D Zn-TCPP(Fe) NSs accompanied by the reduction of ox-TMB production. Our proposed sensing system exhibited favorable selectivity and sensitivity (LOD of 0.029 mU/mL) and has excellent potential to evaluate AChE activity in human serum samples and to screen AChE inhibitors. This colorimetric assay could provide an alternative pathway for early diagnosis and drug screening of AD, facilitating the development of AD therapy.