Objective: To find if there is a significant increase in liver span by ultrasound after 2 and 5 months of using doxycycline 100 mg daily as malaria prophylaxis among the Jordanian contingent working with the United Nations in Liberia. Materials and methods: Ultrasound was done to the 115 people in the contingent before starting doxycycline, and repeated after 2 and 5 months. Liver span was recorded. A total of twenty four persons were excluded from this study population. Results: Liver span ranges from 13.6 to 16.8 cm at the beginning. The change in span ranges from -0.1 to 0.5 cm in the first two months and -0.1 to 0.9 cm after 5 months from the zero readings. The average liver span at zero time was 14.99 cm, and increased to 15.20 after 2 months and to 15.25 after 5 months. Conclusion: The increase in liver span after the long term use of doxycycline 100 mg as antimalaria prophylaxis, was statistically not significant (P value 0.00), and it happened mainly in the first two months of using it.