Purpose: This study aimed to compare the viscoelastic properties and antimicrobial activity of a soft liner with and without silver zeolite for a period of 4 weeks. Materials and Methods: Thirty edentulous patients wearing complete dental prostheses were selected. A uniform space was created in the intaglio surface of their maxillary prosthesis, and a soft liner without silver zeolite (control material: S) was applied. After 28 days, the soft liner was replaced with new soft liner containing silver zeolite (test material: SZ) and worn for another period of 28 days. Viscoelastic analysis was conducted on the prostheses using S and SZ materials for newly formed samples (T0) and on samples collected after the 28-day period (T28). Culture tests were performed on both materials at T28. Statistical analysis was done using Student independent t test. Results: The decrease in elasticity from T0 to T28 was found to be 76.49% and 79.11% and the decrease in viscosity was 76.49% and 80.3% for the S and SZ materials, respectively. Hence, the difference was not significant. The mean colony-forming units (CFUs) of Candida albicans and gram-negative bacteria in the S material at T28 days was 3,150 ± 1,251, whereas that of the SZ material was 1,084 ± 662. There was a statistically significant difference in the mean CFUs between the two groups (P .05). Conclusions: The addition of silver zeolite to the soft liner improved the antimicrobial activity while not affecting significantly its viscoelastic properties.