The growth and yielding of crop plants depend on weather conditions during the vegetation period. Air temperature is among the main meteorological factor which affect the level and quality of wheat crop yields. Measured values of extreme air temperatures (minimum and maximum) used in this text had been recorded at meteorological stations in Tomaszów Lubelski, Werbkowice and Zamość, and the quoted results of phenological observations were collected from arable fields of the Zamość region in the years 1976-1995. The materials collected were used for the calculation of the maximum and minimum air temperatures in 3 periods: from start of spring vegetation till stem elongation stage, from stem elongation to heading phase, and from heading till the dough maturity phase of winter wheat. The earliest start of spring vegetation was observed in the 3rd decade of February and the latest in the 1st decade of April. The dough maturity phase was usually attained by winter wheat in the 3rd decade of July. The earliest dough maturity was observed in the 2nd decade of July, and the latest in the 1st decade of August. Average air temperature in Zamość region during the period from start of spring vegetation till dough maturity of winter wheat was 12.9oC, with minimum average of 7.3oC and maximum of 18.5oC. The minimum and maximum air temperature values had an enormous influence on the length of the periods from stem elongation phase to heading phase, and from heading till dough maturity, the stronger effect being that of the maximum air temperature.