The aim of this study was to investigate the influence of cultivar and harvesting time on the chemical composition in tubers of Jeruzalem artichoke (Helianthus tuberosus L.). The tubers of two cultivars (Albik and Rubik) come from cultivation carried out between 2000-2002 in Plant Breeding and Acclimatization Institute in Radzików (Poland). They were collected two times per year, in autumn and spring after winter storage in soil. Content of dry matter, protein, ash, glucose, fructose, saccharose, fructan, dietary fiber, vitamin C, polyphenols, nitrate(V) and (III) in tubers was determined. As a result it was found that the chemical composition depends on cultivar and harvest term. In tubers collected in spring the significant increase in glucose, fructose, saccharose, dietary fiber, polyphenols and nitrate(V) content was notified. Fructan, vitamin C and nitrate (III) content was higher in tubers collected in autumn.