The aim of the study was to assess the basic chemical composition of new varieties of winter squash and studying of changes in contents of these compounds during the storage. Experimental material determined 2 new varieties (Justynka i 958) and 1 variety registered long time ago (Bambino) of winter squash. Plants were grown in the experimental field “Wolica” of Faculty of Horticulture and Landscape Architecture of Warsaw Agricultural University. Fruit harvest was conducted in 21 September 2005. Researches were conducted directly after the harvest and in three periods of storage II – after 4 weeks after the harvest, III – 8 weeks and IV period – 12 of weeks after the harvest of fruit. Pumpkins were stored at first in the folic tunnel, and next in the cold storage room at 10ºC and 75% humidity. The content of the dry matter and suluble solids in new varieties of the winter squash were over twice higher than in the traditional variety Bambino. Directly after harvest the content of total sugars in investigated varieties were differed, however for 12 weeks of storage statistically essential differences weren’t noted. The highest content of total carotenoids and β-carotene from among given an examination varieties were marked in the new variety Justynka, instead in Bambino lowest. Sunny sides of fruit of the winter squash were contained the higher dry matter, soluble solids, total sugars, total carotenoids and β-carotene in comparison to shadow side of the winter squash.