I have studied the relation between the global star formation activity and the bar structure in a sample of isolated barred galaxies. The star formation activity was quantified via the ratio between the IRAS fluxes at 25 mu m and 100 mu m. Two parameters were chosen to define the bar structure: the strength of the bar and the relative projected bar length. The strength of the bar was defined by epsilon_ {b}=10(1-b/a), where a and b are the projected semi-major and semi-minor bar axis. The relative bar length was defined as: 2Lb/D25, where L_ {b} is one half of the projected total bar length and D25 is the diameter of the 25 mag arcsec-2 magnitude isophote in the B band. We found a strong correlation between the star formation activity and epsilon_ {b}. The regression line is given by log(I25/I100)=-1.81+0.093 epsilon_ {b}, with a correlation coefficient of 0.9. The link is not so evident between the relative projected bar length and the star formation activity. But, it is noted that there is enhanced star formation activity in galaxies with strong bars and small relative bar lengths, 0.1<2Lb/D25<0.22.