This manuscript deals with successful trials to isolate two lichen acids (Noristicic and Everinic acids) from natural sources. The isolated compounds were purified, crystallized from suitable solvent, and their melting points were measured. Their structures were identified by elemental analyses, spectroscopic tools (Electronic spectra, FT-IR, Mass), and finally using thermal analyses (TG, DTG and DTA). Their thermal fragmentation pathways were compared with mass fragmentation. These fragmentation pathways were compared with the theoretical molecular orbital calculations (DFT- MOCs). The molecular structures of the title compounds in the ground state were optimized by a DFT method using B3LYP functional combined with 6-311G** (d) basis set. Calculations were carried out using GAUSSIAN 09 suite of programs. In addition, antioxidant activity of norstictic acid and everinic acid were determined. The results showed that both compounds exhibited antioxidant activity, but that the norstictic acid showed several times higher activity than evernic acid. This study refers to successful obtaining of these biologically active acids from natural sources and of wide biomedical applications.