The purpose of this thesis was to examine the influence of solar flares on radio waves propagation through the ionosphere. The ionosphere is made of plasma which indicates the existence of electric charge. That charge can influence radio waves propagation. Charge distribution is non-uniform, it is layered and different layers have different charged particle densities and contain different types of ions. Some layers disappear at night or the density decreases, which leads to decreased radio waves atenuation and the intensity of the radio signal increases. During the day, intensity decreases. The magnetic activity of the Sun follows a quasy-periodic, approximately 11 years long cycle, during which the magnetic polarity reverses. The solar activity influences the state of the Earth's ionosphere. During the solar cycle maximum, solar flares occure more frequently. Each flare realeases an amount of energy, in the form of high frequency radiation, high enough to instantly cause changes in the Earth's ionosphere. In this thesis we have analised the time interval from September 2014 to March 2015, the maximum of the 24th solar cycle, by analyzing the data obtained by three SID (Sudden Ionospheric Disturbance) monitors. The solar flares can be detected on a radio signal in a form of a sudden and relatively short signal change. Both decrease and increase in the signal intensity can occure. The influence of the are is more easily seen during the day when the intensity is showing lower values. Some flares, within the highest energy range (7000−20000 keV) were detected on each of the three monitors. Lower energy flares (100 − 300 keV) were detected on a single monitor. Geomagnetic activity for each of the studied solar events was also analysed.