I obtained my single entry visa in French Embassy in Dubai for 15 days, Currently I am here in France and I am planning to travel in Spain for five days then go back again in France. Would it be possible for me to travel to Spain since I am holding Single Entry Visa?
you might try the right forum for an answer.
Take the advice above about asking the Embassy, but most likely what you have is a Schengen area visa issued by the French embassy. In that case, since Spain is part of the Schengen Treaty and you do not need to leave the Schengen zone to get there, you would be able to travel to Spain and back without it being considered a "re-entry"