We examined the effect of salt stress on seedling growth, cell morphologic features and ultrastructure, as well as ion uptake and distribution for poplar seedlings of Nanyang 1 and 2. Under low salt stress (75 mmol·L^–1NaCl), the growth inhibition was greater for Nanyang 1 than 2. Under high salt stress (150 mmol·L^–1NaCl), growth inhibition did not differ between the 2 poplar strains. Low salinity produced greater damage to cell morphologic features and ultrastructure for Nanyang 1 than 2. In Nanyang 1, chloroplasts were bent and separated from the cell membrane, and the starch granule size was smaller and even absent. However, under high salinity, the damage was visible in both poplars. X-ray microanalysis revealed higher Na⁺ content in root cells of Nanyang 1 than 2 with salt stress, especially low stress. Under salt stress, in a new branch, Na⁺ content in epidermis, cortex and xylem cells was higher for Nanyang 1 than 2. In roots and new branches, Na⁺ distributed first in epidermal and cortical cells of both poplars, which indicated that roots and new branches had strong Na⁺ retention; nevertheless, we observed slight or no significant Na⁺ increase in both poplar leaves. Under salt stress, in leaves, Na⁺ content in upper epidermis, palisade and spongy cells was higher for Nanyang 1 than 2, and except for upper epidermis cells, the Mg²⁺ content in the other cells was higher for Nanyang 2 than 1. In general, as compared with Nanyang 1, Nanyang 2 could maintain lower Na⁺ content in all root cells; the epidermis, cortex and xylem cells of new branches; the upper epidermis, palisade, and spongy cells of leaves; and palisade and spongy cells. Na⁺ flow to branches and leaves was lower in Nanyang 2 than 1. Thus, ionic homeostasis ability was greater in Nanyang 2 than 1 and may explain why Nanyang 2 has higher salt resistance than Nanyang 1.