Biological photovoltaics (BPVs) are emerging as a potential sustainable energy-generating technology to convert solar energy into electrical energy. Although a great variety of photosynthetic biomaterials were studied in BPVs, cyanobacteria are considered as superior candidates because of their simpler physiology. To facilitate extracellular electron transfer (EET) from cyanobacteria to electrodes is the greatest challenge to improving the performance of BPVs. However, a systematic study comparing the photo-excited EET from such organisms is not yet reported. Here we report on a comparison of photocurrent density generated by benthic cyanobacteria, that is, two species of Leptolyngbya sp. (CAWBG62 and CAWBG100), one species from the order Chroococcales (CAWBG64), and a eukaryotic algae, Paulschulzia pseudovolvox (UKE). This algae and CAWBG100 were sourced from New Zealand, CAWBG62 and CAWBG64 were from Antarctica. We demonstrate EET mediated by three different electron transfer (ET) mediating systems on graphite electrodes. These are as follows: (I) [Os(2,2'-(bipyridine)(2)(polyvinyl-imidazole)(10)Cl](+/2+) (1:9) [Os-(bpy)PVI] (II) p-benzoquinone (PBQ) (III) [Os-(bpy)PVI] together with PBQ. The maximum photocurrent density of 47.2A cm(-2) was obtained from CAWBG64 mediated by (III) [Os-(bpy)PVI] together with PBQ.