The purpose of the study is to investigate factors influencing the accuracy of specialist sub-contractors cost estimate in public construction projects. To achieve this, the researchidentifyfactorsaffecting the accuracy of the estimate, methods used and people involved in preparing specialist sub-contractors cost estimation. The population for the study included 91 quantity surveyors working in public and private organization. Convenient sampling technique was used in selecting the respondents. A cross-sectional survey was conducted within the Birnin-Kebbi metropolis.The data collected were subjected to mean score analysis. Three significant factors were identified as influencing the accuracy of specialist sub-contractors in the study area, namely; quantity surveyors exclusion in preparing special sub-contractors estimate in building projects (8.7%), sources of cost information (7.7%) and level of experience of the quantity surveyor (7.5%) respectively. Cost estimating for special subcontractors is a neglected area within the construction industry and therefore poses serious challenge to quantity surveyors proficiency in the discharge of his various professional duties.It was concluded that estimation process and other core duties of quantity surveyors particularly in the area of specialist works are graduallytaking over by special subcontractors in the construction industry.Itwas therefore recommendedthat an enlightenment workshop be prepared by the Quantity Surveyors within the regionson the effects of specialist sub-contractors estimations on quantity surveying profession in arriving at reliable and accurate total cost of construction estimation in public and private construction projects. Keywords:Specialist,accuracy,factors,construction,Quantity Surveyor