We characterized differences in cell wall material and polysaccharide structures, due to the quantitative trait loci associated with higher flesh firmness in a nonclimacteric near-isogenic line (NIL) SC7-2, and with the climacteric behavior of the NIL SC3-5-1, using their nonclimacteric inbred parentals, "Piel de Sapo" (PS) and PI 161375 (SC). PS was firmer and had a higher ripening index and greater hemicellulosic content than SC, with its lower wall material yield, and uronic acid, neutral sugar, cellulose and free sugar content and higher pectic content. SC3-5-1 showed lower uronic acid values, a higher soluble solid content, and similar flesh firmness to PS. SC3-5-1 yielded mainly high molecular weight polysaccharides in the imidazole-soluble fraction than PS. SC7-2 showed greater flesh firmness, a higher neutral sugar (especially galactose and mannose) and uronic acid content, together with a larger cellulose and α-cellulose residue than PS. SC7-2 also contained more polysaccharides of low molecular weight in the first pectic fraction and shifted toward higher molecular weights in the main peak of the 4 M potassium-soluble fraction compared with PS.