Seasonal changes in photosynthetic rate and the vertical distribution of chlorophyll content were measured at the center of Lake Shinji, Shimane Prefecture, Japan, from May 1994 to November 1995 at monthly intervals. The chlorophyll content was almost similar from surface to bottom water layers, and the maximum, mean ± SD and minimum values of chl. a (mg /m^2) were 341.4 (13 October 1994), 132.7 ± 80.7 and 41.6 (20 April 1995) , respectively. Net Photosynthetic rate showed a highest value in October 1994 and showed a negative value in February 1995. Seasonal changes in the vertical profile of some water variables such as transparency, pH, dissolved oxygen content, water temperature, conductivity, salinity, C1^-, relative light intensity are also reported.