Abstract: Ultraweak luminescence from zebra fish (Brachdanio rerio Ham. et Buch) was measured with a highly sensitive single-photon counting system. Spectral lines emitted from fish were 357, 370, 401, 512, 573, 596 and 635 nm. Photon count rate (hv穝-1) declined over time and finally reached a steady level. Photon emission from the fish was affected by pH of the media and duration of oxygenation. Scrapping of scales did not affect the natural ultraweak luminescence, but affected the NaN3-induced luminescence. In addition, data were presented on the surface area of the zebra fish in relation to body length. The accuracy of measuring the ultraweak luminescence was described.