BACKGROUND: Although Cast Chromium Cobalt alloy has been the material of choice for fabricating Removable Partial Dentures (RPDs) but it has certain drawbacks. New material like the flexible Nylon based Super Polyamide has been introduced to overcome these drawbacks. The present study compared the above two materials for three clinical parameters. MATERIALS AND METHODS: The study was carried out on 15 patients, the selected cases were Kennedy Class I, with missing teeth first, second and third molars in each distal extension side. These fifteen patients received three RPDs; each one was used for six months. Three types of RPDs were made from different base materials; cobalt chromium alloy and thermoplastic denture base materials, (Group A): RPDs made of cast Cr-Co alloy incorporating RPI clasping system with denture base made of heat cured acrylic resin. (Group B): RPDs made of flexible nylon based super polyamide resin incorporating flexible circumferential clasps and denture bases made of flexible nylon, with metal occlusal rests. (Group C): RPDs made of flexible nylon based super polyamide resin. After insertion of each denture, their Clinical performances were evaluated periodically for six months for the following parameters (Gingival index, plaque index and pocket depth). RESULTS: Statistically significant results were obtained in favor of flexible RPDs, in the parameters of (Gingival index, plaque index and pocket depth).Both groups B and C showed less similar values for (Gingival index, plaque index and pocket depth). during usage' with the incidence being slightly higher for patients wearing the cast RPDs (Group A). CONCLUSION: Based on the favorable results of this study, it can be summarized that the flexible RPDs is a viable alternative to cast RPDs in Kennedy class I partially edentulous situation in the short term.