This study was undertaken to identify key stress factors among professionals in building construction industry in Nigeria. This is in view of the fact that to date, very little is known about work stress among professionals in building construction industry in this country. The study involved the administration of questionnaire to 107 professionals including architects, builders, civil/structural engineers and quantity surveyors randomly selected from 60 ongoing building projects in Anambra, Ogun and Kaduna States, Nigeria. The data was analysed using descriptive statistics, and findings show that the principal sources of stress were high volume of work, uncomfortable site office environment, lack of feedback on previous and ongoing building projects, and variations in the scope of work in ongoing building projects. The paper suggests that taking responsibility for work which one has adequate capacity to handle, establishing realistic budgets and time frame for project delivery, provision of spatially adequate, visually and thermally comfortable site offices, adoption of appropriate job design practice and education of professionals on stress management strategies will reduce the incidence of stress among professionals in building industry in Nigeria.