This study aims to (i) evaluate the phenology of Prosopis juliflora (Prosopis), (ii) investigate the effects of climate variability (temperature and precipitation) on the phenology of Prosopis, and (iii) assess the critical months of seed dispersal for the species management. Monthly data for phenology events: leafing, flowering, green and mature pods were collected from 8 stems of Prosopis trees at each of two localities in Ethiopia during 2016/2017. In Amibara district we found that relative abundances of green leaves, flowering, green pods, and mature pods were 91, 15, 9, and 2% in order. However, these were less than by 8, 53, 91, and 90%, respectively in Awash Fenatle district. The lowest proportions of mature and green pods were recorded in the dry season and the highest in the spring season. We recorded the highest and lowest relative abundances of flowering between November and December, and January and February, respectively. In this study, both temperature (F = 2.01, P = 0.04) and precipitation (F = 2.85, P = 0.01) had shown significant effects on the relative abundances of green leaves but insignificant effects on other phenology stages. Higher green leaf abundances were recorded during high rainfall, whereas lower abundances of leaves were recorded in high temperatures. But, the relative abundances of Prosopis leaves showed inconsistent with the variations of precipitation. Thus, awareness creation for stake holders about the phenology calendar of Prosopis should be given to abandon the invasiveness of the species towards the prime grazing lands in the region.