Substances which are normally secondary metabolites in a lichen are known to possess various medicinal properties but little is known about the biological activities of compounds present in these mycobiont culture extract. The objectives of the present study were isolation and optimization of growth conditions of the mycelia from Parmotrema austrosinense and assess the antiproliferative and antimicrobial activities of acetone extracts. The extraction of bioactive compound from mycobiont culture was achieved by using acetone and standard Soxhlet extraction procedures. The culture extract was subjected to silica gel column chromatography and detection of compound in thin layer chromatography. HPLC, UV vis, IR spectra, microcrystallization and NMR were done for the purified compound. The antimicrobial activity in the extracts were assayed using the standard disc diffusion and broth microdilution protocol against microbial strains. The lecanoric acid in the extracts was purified and MTT method was applied to assess antiproliferative activity against DLA cancer cells. The culture extract containing lecanoric acid exhibited antimicrobial activity against the test strains with the Minimum Inhibitory Concentrations varied between 0.83±0.28 and 2.3±1.5 mg mL−1. The lecanoric acid inhibited the growth of DLA cancer cells with inhibitory concentration (IC50) of about 42±1.5 µg mL−1. Conclusion: The result of the present study suggests that this compound might possess potent antitumor property and should be further analysed using appropriate animal model and clinical trials.