AbstractTwo eucalyptus hybrids (EGC 39, EGC 241), resulting from crosses between Eucalyptus grandis and Eucalyptus camaldulensis, were investigated to see if they could produce kraft papermaking fibers with low lignin and adequate physical properties. The two hybrids were harvested at an age of 8 years along with 6-8 year old Eucalyptus camaldulensis (Rostrata). All three eucalypti were grown in the area of Gharb in the North-West of Morocco. The tracheids in the two hybrids had a very high Runkel ratio (2 x cell wall thickness/lumen diameter) and produced kraft paper sheets with low tensile strength due to a low degree of fiber collapse thus a low relative bonded area. These fibers could be used to increase the stiffness of a papermaking furnish. The lignin in the EGC 39 chips was more reactive in kraft pulping as compared to the other two eucalypti. Methoxyl analyses and nitrobenzene oxidation (NBO) of the in-situ lignin (wood meals) were performed, and it was concluded that the syringyl content of the EGC 39 lignin was less than or equal to those in the other two eucalypti. Differences in the guaiacyl fraction of the three samples will be discussed in Part 2 of this series.