In the present study, cambial activity and the differentiation of phloem and xylem was studied in plants of Rosa canina L. growing in the Van province, Turkey. This species belongs to the dogroses, which are frequently harvested for their fruits (rose hips). The cambial zone was up to three cells wide. Cambial activity started in the third week of April. Summer wood formation was observed toward the end of May. The mean length and width of cambium cells during spring wood formation was 15.06 mu m and 2.70 mu m, respectively. During the summer wood formation, length and width was 14.16 mu m and 3.16 mu m, respectively. In spring wood, the lumen diameter of the biggest vessel was 54.41 mu m, whereas the smallest one was 9.58 mu m. The equivalent measurements in summer wood yielded 44.16 mu m and 9.58 mu m, respectively. The mean cell wall thickness of vessels and tracheids in spring wood was 1.87 mu m and 3.33 mu m, respectively, and 2.08 mu m and 5.41 mu m in summer wood. Cambial activity ceased toward the end of July.