Hourly mean values of X, Y and Z components of the geomagnetic field from two observatories and the total intensity, F, of the geomagnetic field from eight monitoring stations were analysed to study the behaviour of solar and lunar geomagnetic variations in the northwestern part of Turkey. The ChapmanMiller method was applied to the data first as a whole and then by grouping it to Lloyd's seasons to calculate seasonal dependence of the harmonics. Amplitudes of solar and lunar harmonics increase from winter months to summer months. The first two harmonics of both solar and lunar origins were calculated annually to compare with sunspot relative numbers to see annual and semi-annual variation. The solar harmonics show very good sunspot dependence, but lunar harmonics do not. It means that both ionospheric and ring current systems have an important role in the formation of solar harmonics, but lunar harmonics are affected by ionospheric current system only in the northwestern part of Turkey. We would not expect and we do not find much ocean effect at these observatories since they are all remote from oceans with significant tides.