Mycosporine-like amino acids (MAAs) are considered efficient photoprotectants against high energy UV-photon flux. The present study is intended to probe the occurrence and synthesis of UV-absorbing MAAs and characterization of their induction, stability and free radical scavenging capacity in the cyanobacterium Nostoc sp. R76DM. HPLC-PDA detection, and LC–MS analysis revealed the occurrence of four different MAAs, palythine (λmax 320 nm, m/z 245), Asterina (λmax 331 nm, m/z 289), Porphyra (λmax 333 nm, m/z 347) and palythene (λmax 359 nm, m/z 285) with retention times 2.9, 4.71, 6.29 and 7.05 min, respectively. Induction of the synthesis of all MAAs was highly noticeable under UV-B radiation. These MAAs were exceedingly resistant to some physico-chemical factors such as UV-B, temperature, pH and a strong oxidizing agent. Total MAAs were extensively evaluated for their antioxidant properties by 2,2-diphenyl-1-picryl-hydrazyl, ferric reducing antioxidant power, superoxide radical scavenging and reducing power assay. MAAs exhibited significant and dose-dependent in vitro antioxidant and in vivo ROS scavenging potentials. Moreover, the results indicate the vital role of MAAs in life-saving mechanisms of cyanobacteria by virtue of their UV-absorbing/screening and antioxidant function. The results also added up evidence in favor of MAAs for possible use as active ingredients in cosmeceuticals.