This work evaluated the effect of different concentrations (5, 10, and 20%) of Bordeaux mixture (Bm) in the diet of the silkworm caterpillars in order to improve the cocoon production and structural and mechanical properties of the ensuing silk. The cocoon yield, tensile properties, and microstructure (X-ray diffraction, surface fracture, and qualitative composition) of the obtained silk fiber threads were determined. The mortality levels of caterpillars fed on mulberry leaves with Bm were up to 80% higher than the rates observed on caterpillars fed on non-treated leaves. The consumption of leaves decreased as the amount of Bm introduced to the caterpillars' diets was increased. However, the lower demand of leaves by caterpillars fed on leaves treated with 5 and 10% of Bm did not imply in obtaining lower cocoon productivity, as the raw silk rates were not different in comparison to the control group. The tensile strength and maximum strain of the fiber were greatly improved, whereas the toughness was not statistically improved by the presence of Bm in the diet. There was an increase in the concentration of Ca and Cu in the silk fiber threads treated with Bm, leading to higher crystallinity. If the cocoon producers were rewarded with an increase in cocoon quality, the application of Bm could be interesting, despite the increase in caterpillars' mortality.