The construction industry in Nepal is an important sector due to its enormous contribution to the country’s economic development. This in terms of employment opportunities and attraction of Foreign Direct Investments which grossly contributes to the country’s GDP. Due to various factors many construction projects are prone to delay. These delay factors can only be avoided by first identifying the factors and their sources. The objectives of this research were to find out the causes of delay and to find related importance in completed Road construction projects in SNRTP in Gandaki province in Nepal. The Relative Importance Index (RII) was used to rank the causes of delay. Similarly, reliability of research instrument was calculated using Cronbach’s coefficient alpha. The results obtained indicate that the top major causes of delay were; weather and climatic condition (RII=0.898), delay in decision in relocation of service (RII=0.886), long chain of hierarchical decision making process (RII=0.885), land acquisition/donation (RII=0.884), inaccurate time estimation, errors during construction (RII=0.884), conflict between joint ownership of the project (RII=0.872), poor communication and coordination between the participants (RII=0.836), lack of database and experience for estimating activity duration and resources required in a construction (RII=0.818) ,owner’s lack of experience and involvement (RII=0.809), shortage of materials /equipment (RII=0.807), improper project document management (RII=0.800), to least ranked consultant’s reluctance for change and their flexibilities (RII=0.722) .Finally the top major delay mitigating measures were; Information sharing and Joint risk management, Enhancing Contractual management and administration capability, Making timely decision in project, Managing sufficient time and allocation of adequate team for project preparation, Completing pre-execution preparation of project before project starting, Investigating/studying the site properly, strengthening the skill/capability of human resources and selecting better Time for contract.