Construction is a complex and challenging activity owing to the technical advances, tighter regulations and need for effective management of resources for competitive edge. The projects under the industry involve many parties namely the contractors, consultants, clients, suppliers, subcontractors and other project parties.. Studies carried in Kenya have established relationship between; hiring skilled manpower and timely completion of projects, skilled manpower and quality project output, timely release of funds and project completion and supervision style and quality projects. However, none of the studies have considered the relationship between contractors and subcontractor in project delivery which is the area of interest in this study. Further, the government enactment of stiff policies and regulations to enhance quality project delivery and mutual relationship between contractors and subcontractors has not borne fruition as government continue witnessing an alarming stalled or poor quality projects. The objective of the study is to identify and categorize the most common factors used by general contractors in the selection of suitable subcontractors for project implementation in Nairobi area. The multiple comparative case study design and a population of 70 firms were used. The response rate of the study was 81.5%.The results revealed that, "Compliance with regulations" was ranked in the first position by both the contractors and subcontractors with RII of (0.808). Also, each of them separately ranked it in the first position with RII of (0.778) and (0.838), respectively. This emphasizes that, this is the most important factor used by general contractors for selection of suitable subcontractors in this group, since the knowledge and compliance with regulations reduce the problem. The study recommends the contractor selects the subcontractors according to their experience, capabilities, resources and reputation. The study may help various relevant government agencies in policy formulation.