Investigations of chlorophyll a and primary productivity were carried out in the Chukchi Sea and its northern Chukchi Plateau during the 2nd Chinese National Arctic Research Expedition in the summer of 2003. The results showed that the chlorophyll a concentrations were 0.009-30.390μg/dm³ at the surveyed waters; the surface chlorophyll a concentrations were 0.050-4.644μg/dm³ and the average value was (0.875±0.981)μg/dm³ in the surveyed area. In the continental shelf of the Chukchi Sea, the chlorophyll a concentrations at the depths 10m to bottom were higher than that in the surface water, and the concentrations were lower at the depths below 75m in the Chukchi Plateau, with average value of (0.015±0.007)μg/dm³ at the depth of 200m. The chlorophyll a concentrations decreased in 3 sequential samplings on the Section R, with column water average values of (2.564±1.496)μg/dm³，(1.329±0.882)μg/dm³ and (0.965±0623)μg/d3, respectively. The potential primary productivity in the Chukchi Sea ((2.305±1.493)mgC/(m³•h)) was higher than that in the Chukchi Plateau ((0.527±0.374) mgC/(m³•h)). The assimilation number of photosynthesis was (122±114)mgC/(mgChla•h) in the surveyed stations. The results of the size-fractionated chlorophyll a and primary productivity showed that microplankton accounted for the majority of the total chlorophyll a (63.13%) and primary productivity (6516%) in the Chukchi Sea. The contributions of the nanoplankton and picoplankton to the total chlorophyll a and primary productivity were roughly the same; the average contribution rates for the total chlorophyll a were 19.18% and 1769%, respectively; and the average contribution rates for the total primary productivity were 20.11% and 1473%, respectively.