The paper deals with the comparison of observations by the Irkutsk incoherent scatter radar (ISR) during the period of 1998–2003 with predictions of the International Reference Ionosphere model, IRI-2001. For the comparison, we used data for only magnetically calm days (K p ⩽4). Our study showed: (1) good agreement between IRI and ISR data during the equinoxes for the electron density N e , electron temperature T e and ion temperatures T i ; (2) during daytime hours in summer the model overestimates the measured electron densities by 30–50% and underestimates the electron temperatures by 400–800K, in winter, on the other hand, the model predictions of electron density are lower by 15–25% and are larger than the measured electron and ion temperatures; (3) during winter the radar shows a night enhancement in N e at predawn, while the model predicts a weak enhancement near midnight.