Palm-leaf manuscripts, which use palm leaves as the recording medium, possess significant documentary and research value. Existing palm-leaf manuscripts suffer from various deteriorations, with contaminants being one of the common issues. This study selected four brown-black contaminants from the surfaces of three palm-leaf manuscript artifacts as research subjects. Comprehensive analytical techniques including optical microscopy (OM), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), gas chromatography-mass spectrometry (GC/MS), and X-ray diffraction (XRD) were systematically employed to analyze the chemical composition of the contaminants. Experimental results indicated that all four contaminant samples primarily consist of aged and degraded oil mixtures with dust, and molds and calcium soaps were found in some of the samples. Based on the analytical findings of the brown-black contaminants, online thermal aging-headspace gas chromatography-mass spectrometry (Headspace-GC/MS) analysis of mock-up samples preliminarily revealed the impact of oil contaminants on the durability of palm-leaf materials. The research outcomes provide scientific basis for the selection of cleaning materials for palm-leaf manuscript contaminants and the formulation of cultural heritage conservation strategies.