The present study makes a comparison of the amount of direct solar radiation and its extinction in Warsaw and in Mikołajki. The input material was sourced from the results of measurements recorded by the Institute of Meteorology and Water Management (IMGW) in the years 1960-2003. In this study, only those days are considered when the measurements were taken at both stations. For each station, the amount of solar radiation reaching the surface of the Earth was determined in relation to the solar constant and the spectral composition of the radiation was presented. The extinction of direct solar radiation was expressed by means of Linke’s turbidity factor reduced to the atmospheric mass of 2 (TLAM2). The average amount of solar radiation in relation to the solar constant recorded for the reference period was bigger in Mikołajki. Also, the mean turbidity factor indicates a smaller extinction in Mikołajki (TLAM2 = 2.86) when compared to Warsaw (TLAM2 = 3.19). In an annual course, the highest values of TLAM2 are observed in spring (Warsaw) or summer (Mikołajki), and the lowest in winter (at both stations). The optical state of the atmosphere was also evaluated depending on the type of prevailing air masses. For all distinguished air masses, the atmospheric turbidity was bigger in Warsaw than in Mikołajki. It is a characteristic feature of both stations that the highest turbidity occurred in tropical air masses and the lowest in arctic air masses. The continental type came out as the most turbid of all polar masses.