The main objectives of this paper are to get a better understand of the rainfall space-time variability and to assess its rainfall tendency in the Merguellil basin, central Tunisia, by means of statistical tests. We assessed the rainfall at seasonal and monthly scales. Based on the availability of a continuous good record, eleven rain gauges were carefully chosen. Monthly rainfall data range from 1980 to 2016. Two tests are used to examine the trends: the non-parametric Mann-Kendall and Sen's slope were selected to detect the existence, with a statistical significance, of an increase or a decrease in rainfall data trend. Results revealed high space-time variability of rainfall showing significant changes in seasonal and monthly rainfall amounts, for the studied period, particularly for summer months. The rise ranges from 0.68 mm/yr to 2.08 mm/yr and the highest values are observed in the basin upstream. Consequently, there are signs of a considerable rainfall raise in the basin. Increasing trends in summer, especially in July and August, were detected in the majority of studied rain gauges, where the monthly upward varies between 0.46 mm/yr and 0.83 mm/year. Most of the calculated slopes are statistically significant and the changes in Merguellil basin are more significant compared to other studies.