The thermopower of single crystalline Bi microwires with diameters ranging from 0.1 to 14 μm were measured in the temperature range 4 – 300 K. Cylindrical crystals with glass coating were prepared by the high frequency liquid phase casting in a glass capillary. The peaks are the dominant features of the temperature dependences of thermopower at temperatures below 12 K. This peak is a manifestation of the phonon drag effect. We observe that the phonon-drag thermopower depends on the wire diameter and increases with increasing diameter of the sample. We have studied the dependence of the phonon drag thermopower on transverse magnetic field and transverse electric field. Effect of transverse magnetic field (B=0.4 T) of various orientation to the phonon drag thermopower is negligible for Bi microwires d<0.6 μm but quickly arise for Bi microwires d>1.5 μm. This means that in fine Bi microwires at low temperatures mobility of electrons are much smaller than holes (due to strong surface scattering of electrons on surface roughnesses). Influence of transverse electric field to the phonon drag thermopower of Bi microwires is very small.A possible explanation of these experimental results is presented.