Parthenium weed (Parthenium hysterophorus L.), an invasive alien species, has been spreading at alarming rate in Ethiopia, causing biodiversity degradation, yield losses in field and horticultural crops, health problems to human beings and livestock. A study on the socioeconomic and ecological impacts of P. hysterophorus was conducted in five Kebeles (lowest administrative division) of Boset Woreda (District), Ethiopia. Data was collected using Ecological Survey, Semi Structured Interviews, Focus Group Discussion, and Field Observations. 200 quadrats were employed where every plant species found in each quadrat were counted, recorded and identified. Data on informant's perception about the first appearance, infestation levels, agents of dispersal, impact, and cultural management of the Parthenium weed were analyzed using descriptive statistics. Shannon Diversity Index (H′), Species Richness, Evenness, and Jaccard's Similarity Index were executed to evaluate Parthenium's effect on species diversity of the weed flora. 78 Herbaceous plants belonging to 59 genera and 21 families were collected. Poaceae (28.2%) and Asteraceae (16.7%) were the dominant families of weeds observed in the study Kebeles. Digalu and Merko Kebeles had high infestation of P. hysterophorus represented by high distribution, abundance, and dominance of the weed, but with corresponding low Richness, H′, and evenness of herbaceous plants. Species Richness of herbaceous flora and abundance of Parthenium weed reveled significant negative association (P < 0.01; R 2 = 0.93). Most of the informants believed that Parthenium affected crop and livestock production as well as human health. Farmers employed hand weeding, plowing, and manual clearing to manage the weed. For effective use of the weed, Integrated Weed Management approaches are required to check the spread and reduce the adverse impacts.