Site investigation is important in determining the type and the depth of foundation, bearing capacity, water table level, probable problems in soil foundation, lateral earth pressure and construction method of foundation. Site investigation is a must in Nablus City due to Palestine engineering Association and Municipality laws. However, many engineers and contractors do not like to perform site investigation. A questionnaire was distributed to many owners, engineers, consultants and contractors of buildings to shed lights on site investigation in Nablus City. It was found that most people do site investigation for their building had no problems regarding foundation. However, some building faced geotechnical problems due to not performing site investigation, such problems are swelling and slope instability. As recommendation of this project, site investigation should be done for all structures. Moreover, its cost is considerably cheap comparing to the total cost of the structure and if geotechnical problems may occur and try to fix them.