In this paper the relationship between ground temperature and ambient air temperature is investigated in Northern Greece. To this end, 10 years records of daily average values of ambient air, bare and grass-covered ground surface, and ground under bare surface temperatures at depths of 0.02, 0.05, 0.10, 0.20, 0.50,1.00 and 1.50 m measured by the Meteorological Station of Aristotle University of Thessaloniki are used. Seasonal variation of surface and ground temperatures, time lag regarding ambient air temperature variations, as well as the vertical distribution of ground temperature up to 1.50 m, are examined and analyzed. The ground-to-air temperature relation is examined by correlation of average daily, as well as monthly values, and best trend lines equations are defined in order to be used in technical applications. The defined analytical equations are evaluated by comparison of calculated and measured ground temperature values and a very good fitness is found. (C) 2014 Elsevier Ltd. All rights reserved.