There is a lack of randomized controlled trials to compare the outcome of specific questions related to number of implants and design of the superstructure for maxillary palateless implant overdenture. so the aim of the research is To evaluate and compare clinical retention, implant stability and peri-implant soft tissues changes of maxillary palateless implant overdenture assisted by four implants installed in the canine and second premolar areas. Method: six healthy completely edentulous patients were selected to received four implants installed in the canine and second premolar areas and classified into two equal groups as follow: group I: who had sufficient restorative space at least 14 mm received maxillary palateless implant overdenture retained with triple bar-clip attachment while group II: who had restorative space less than 14 mm received maxillary palateless implant overdenture retained with locator attachment. clinical retention was measured by digital forcemeter, implant stability was measured by periotest device and peri- implant soft tissue changes were evaluated at overdenture insertion, after 6 months and after 12 months. Results: Locator recorded significant higher retention forces than bar at all observation times, for anterior implants, bar recorded significant higher implant stability than locator at all observation times. For posterior implants, bar recorded significant higher implant stability than locator at T12 only and no difference in implant stability between groups was noted at T0 and T6, for anterior and posterior implants, bar recorded significant higher probing depth, bleeding index and plaque index than locator at T6 and T12. No difference between groups was noted at T0. Conclusion: The clinical retention of four implant assisted maxillary palateless overdenture was recognized as being accepted for the patient regardless the attachment design used. However, locator attachment recorded higher retention values than bar attachments after all observation period, bar recorded maintained the implant stability compared with locator but need high strict oral hygiene measures.