Plant pathogenic biocontrol agents in the very wide-ranging sense encompass the methods for utilization of organisms except for human. Among all the microorganisms, cyanobacteria and algae are distinguished bioactive agents which have gained a remarkable consideration by scientists globally. Cyanobacteria, autotrophic blue-green algae which are known to be the most diverse, largest and abundantly distributed group of small, prokaryotic, unicellular and photosynthetic organism, found specifically in fresh and marine water, all together with eukaryotic algae ‘could have been the world’s largest biomass’, whereas algae were found either in marine or in freshwater habitat with a large number of species found in soil. They are mostly photosynthetic; however, a great number are heterotrophic facultative species while few are non-photosynthetic/heterotrophic obligates. Both cyanobacteria and algae were used hardly as beneficial extracts against pathogenic fungus because of their stimulation effect for plant productivity and vigour. They have also been used as media substrates for microbial cultures. Cyanobacteria function as the most significant source of naturally occurring bioactive compound with antiprotozoal, antimicrobial, antibacterial, antiviral, anti-proliferative and anticancer activities. Anabaena, Microcystis, Nostoc and Calothrix have been observed to counter inhibitory effect against various fungal pathogens, and also several other species, i.e. Noscomin and Nostocarboline, were found to exhibit antibacterial activity and inhibit the growth of cyanobacteria. Both cyanobacteria and algae have shown a significant role against various fungal and bacterial infections, working as plant pathogens’ biocontrol agents.