An efficient green method of gold nanoparticles (AuNPs) biosynthesis was achieved by cell-free extracts of fungus Trichoderma sp. WL-Go. Based on UV–Vis spectra, AuNPs biosynthesised by cell-free extracts with 90 mg/l protein exhibited a characteristic absorption band at 556 nm and was stable for 7 days. Transmission electron microscopy images revealed that the as-synthesised AuNPs were spherical and pseudo-spherical, and the average size was calculated to be 9.8 nm with a size range of 1–24 nm. The AuNPs illustrated their good catalytic activities for reduction of nitro-aromatics (2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2-nitroaniline, 3-nitroaniline) with catalytic rate constants of 7.4 × 10−3 s−1, 10.3 × 10−3 s−1, 4.9 × 10−3 s−1, 5.8 × 10−3 s−1, 15.0 × 10−3 s−1, respectively. Meanwhile, the AuNPs also showed excellent catalytic performance in decolourisation of azo dyes with decolourisation efficiency from 82.2 to 97.5%. This study provided a green gentle method for AuNPs synthesis as well as exhibiting efficient catalytic capability for degradation of aromatic pollutants.