Scytonemin, a potent UV sunscreen and antioxidant, can be exploited in pharmaceutical industries to develop new cosmeceuticals and medicines. This small hydrophobic alkaloid pigment can be exclusively synthesized in some ensheathed cyanobacteria in complex interplay of various stress factors. In this study, the capacity of marine cyanobacterium Leptolynbya mycodia in scytonemin synthesis under diverse stressful conditions was investigated in two-stage cultivations. The effects of nitrate deficiency as well as salinity and temperature were separately examined on scytonemin synthesis in 2nd stage of cultivations under P-regime (photosynthetically active radiation) and PU-regime (P-regime combined with ultraviolet radiation (UVR)). Nitrate deficiency (0.1-3 mM) alone could not induce scytonemin synthesis under P-regime, while it promoted synthesis induction under PU-regime without remarkable change in cell growth. Nitrate stress level of 0.5 mM showed synergistic effect on UV-induced cell synthesis response (> 25% increase compared to optimal-nitrate level). On the contrary, salt stress reinforced scytonemin synthesis in the absence of UVR. Combination of salt stress at moderate level (100-200 mM) and UVR resulted in a synergistic effect on scytonemin synthesis (similar to 20%). Under various temperature treatment studies, synthesis was not induced under P-regime and higher scytonemin was obtained under PU-regime and heat shock as much as 10 degrees above the optimum temperature. Based on these findings, neither nitrate limitation nor temperature elevation alone induced scytonemin synthesis in L. mycodia while salinity can induce its synthesis pathway without involvement of UVR. However, scytonemin biosynthesis can be intensified under all examined abiotic stressors in conjunction with UVR.