Invasive alien plant species (IAPS) are major ecological threats affecting biodiversity that alter soil fertility and ecosystem stability in disturbed habitats. The present study was conducted to evaluate the effects of invasive plant species on soil physicochemical properties in agricultural and roadside habitats of Lakhimpur district, Assam, India. Field surveys were carried out during the pre-monsoon, monsoon, and post-monsoon seasons of 2024 using quadrat sampling methods to document invasive species diversity and dominance. Soil samples were collected from invaded sites at 0-20 cm depth and analysed for pH, organic carbon, available nitrogen, and phosphorus using standard laboratory methods. The study provides the first comparative assessment of invasive plant-associated soil properties in agricultural and roadside ecosystems of Lakhimpur district. A total of 14 invasive plant species were recorded, among which Eichhornia crassipes, Mikania micrantha, Chromolaena odorata, and Parthenium hysterophorus showed greater dominance. Invaded soils exhibited higher organic carbon (0.76-0.87%) and available nitrogen (230-260 kg ha-1), whereas soil pH ranged from 5.6 to 6.2, indicating slight acidification. Seasonal variation showed higher nutrient accumulation during monsoon and post-monsoon periods. The findings indicate that invasive plant species significantly alter soil nutrient dynamics and may contribute to ecological imbalance and suppression native vegetation. Continuous monitoring and effective management strategies are necessary to minimize the spread and ecological impacts of invasive plant species in Assam.