The excessive use of fertilizers is detrimental to the soil, water, and human health. The application of bio-stimulants such as concentrated seaweed extract (CSE) in agriculture could be an effective and eco-friendly approach to crop nutrition. Sea weed extracts, natural organic degradable substances, are derived from sea algae. The current study was conducted to evaluate the impact of concentrated seaweed extract (CSE) on mustard crop performance, nutrient use efficiency, and soil health during winter seasons of 2018-2019 and 2019-2020 at Rajasthan Agricultural Research Institute, Jaipur, India. Concentrated seaweed extract (CSE) was the mixture of extracts of both red (Kappaphycus alvarezii) and brown (Sargassum swartizii) seaweed. Application of recommended rates of fertilizers (RRF) along with one, two, and three foliar feeding of different concentrations (0.2, 0.3, and 0.4% v/v) of CSE were studied in Randomized Block Design with 10 treatments in three replications. Application of RRF with three foliar applications of 0.3% CSE at branching, flowering, and siliqua formation stages led to higher plant height, leaf area index (LAI), and chlorophyll content (CC). Effect of CSE on plant height, LAI, and CC were nominal at early growth stage i.e. at 45 DAE (Days after emergence). However, at 90 DAE, CSE embedded treatments led to higher plant height (15.5%), LAI (6.9%), and CC (10.3%) in mustard. Increase in yield of 33.0%, 38.9%, and 41.0% were recorded with three foliar applications of 0.3% CSE along with RRF in comparison to RRF alone. Uptake of macro- and micro-nutrients, nutrient use efficiency, and soil fertility status were improved with application of CSE. Higher return on investment (38.7%) and benefit cost ratio (16.6%) were found with three foliar applications of 0.3% CSE along with RRF than with RRF only. Overall, the current study suggests that the application of CSE has great potential in enhancing nutrient use efficiency and improving the yield and quality of mustard under semi-arid conditions.