This investigation was conducted during 2011/2012 season at Sakha Agricultural Research Station farm and screen-house belongs to Sugar Crops Institute. This investigation was carried out on Kawamera sugar beet cultivar to answer the question of why young Leaves of sugar beet possess a high level of resistance to Cercospora leaf spot? Under artificial inoculation by Cercospora beticola spores (50 × 10³ spores / ml), disease severity, chlorophyll content, losses in both yield and sugar were evaluated in randomized complete block design experiment. Different histological and biochemical factors were measured i.e., size of stomatal apparatus, mineral contents in different leaves starting from heart leaves up to outer leaves of the plant. Results obtained revealed that percent losses of inoculated leaves was 64.15 % in chlorophyll content, 52.05% and 41.74% in root and sugar yields were (respectively. Dimensions of stomatal apertures, diameter and stomata intensity showed that the young leaves were narrow and it has less number of stomata ranged from in inner leaves 115 stomata / mm² up to 331 stomata / mm² in outer leaves. Relative water content (RWC) was determined for sugar beet leaves, data obtained showed that young inner leaves contain less relative water content than mature outer leaves. Moreover, peroxidase activity was higher in the younger leaves than the mature one. Element analysis showed that N, P, Fe, Mn and Cu contents increased gradually from the inner first leaf and reduced in the outer fifth leaf, while the opposite was in potassium and zinc contents. Total phenol compounds were increased after inoculation; while the free and conjugated phenol compounds were higher in the young leaves than the oldest ones. This study clarified the role of leaf age and position in relation to resistance to Cercospora leaf spot disease.