Purpose: This study evaluated the ultimate tensile strength of a tissue conditioner without nystatin incorporation (GI—control group) and the same tissue conditioner modified by the addition of nystatin in two concentrations: GII—500,000 International Units (U) and GIII—1,000,000 U, in which each milligram of the medicament corresponded to 6079 U. Materials and Methods: Dumbbell‐shaped specimens (N= 7) with a central cross‐sectional area of 33 × 6 × 3 mm were produced for the three experimental groups. After polymerization following manufacturer's instructions, specimens were immersed in distilled water at 37°C for either 24 hours or 7 days and then tested in tension in the MTS 810 at 40 mm/minute. Data were analyzed by two‐way ANOVA followed by Tukey's test, at 95% level of confidence. Results: The means (force‐grams (gf) ± standard deviation) of the ultimate tensile strength were: GI—634.29 ± 122.80; GII—561.92 ± 133.56; and GIII—547.30 ± 73.47 for 24‐hour storage, and GI—536.68 ± 54.71; GII—467.50 ± 143.51; and GIII—500.62 ± 159.76 for 7‐day storage. There were no statistically significant differences among the three experimental groups (p > 0.05). The ultimate tensile strength means of all experimental groups after 7 days were significantly lower than those observed after 24 hours (p= 0.04). Conclusions: The results of this study suggest that the addition of nystatin into the tissue conditioner investigated in concentrations below 1,000,000 U did not affect its ultimate tensile strength.