Intercropping of cereals with legumes is an important strategy for the development of sustainable crop production systems, because of yield advantages, greater yield stability and lower risks of crop failure that are often associated with monoculture. A field experiment was conducted during 2021/2022 main cropping season at fogera national rice research and training center with the objective of determining the effect of additive series relay intercropping of grass pea with lowland rice on the agronomic parameters of the component crops, the land use efficiency and the profitability of each intercropping system as compared with sole cropped. The experiment consisted of a factorial combination of four seed proportion of grass pea (25%, 50%, 75% and100% of the recommended seed rate of sole grass pea) intercropped with full seed rate of rice in four Rice: grass pea spatial arrangements (1R:1GP, 2R:1GP, 3R:1GP and; R and GP mixed relay intercropping system). The treatments were arranged in Randomized Complete Block Design with three replications. Data on growth and yield parameters of the component crops were collected and analyzed using SAS-JMP-16 software. Results revealed that seed proportion of grass pea and spatial arrangement and their interaction significantly affected only the agronomic attributes of grass pea when grass pea was relay intercropped with rice in additive series. Land use efficiency in terms of land equivalent ratio and Area Time Equivalent Ratio showed more than unity in all intercropping treatments. Maximum land equivalent ratio (1.99), area time equivalent ratio (1.33) and total land output yield (9887kg -1 ) was higher when full seed rate of rice was relay intercropped with 50% seed proportion of grass pea in 3:1 spatial arrangement. The highest positive monetary advantage Index and the lowest competitive ratio was recorded in 3:1 and 2:1 spatial arrangement in the same cropping system. Indeed, according to the partial budget analysis, 50% of grass pea planted with rice in 3:1 spatial arrangement gave the highest net benefit (33, 5176.79) with the acceptable marginal rate of return (21,428%). Thus, it can conclude that relay intercropping of 50% of grass pea with full seed rate of rice (additive series) in rice-grass pea intercropping at 3:1 spatial arrangement would be recommended for maximum land use efficiency and profitability in the study area and areas with similar agro-ecology