The study carried out the economic analysis of marketing margins of roadside marketers of agricultural produce along major highways in Osun State. It also sought to determine the factors that affect their gross margins. A total of one hundred forty (140) roadside marketers' primary data were gathered utilising a pre-tested interview schedule that was given to each of thirty-five (35) respondents in four distinct locations. Descriptive statistics, gross margin model, and multiple regression model were used to analyse the data collected. The majority of roadside marketers (85.7%) were under 50, married (87.9%), had at least a primary school education (85%), and had less than 10 years of marketing experience (56.4%), according to the research. The roadside marketers were selling commodities which included palm oil, yam, plantain, cocoyam, banana, pineapple, snails, honey and others with the dominant commodities being plantain (77.1%), yam (64.3%) and palm oil (56.4%). The average gross margin of the roadside marketers was estimated at ₦25, 312.90 per month The coefficients of age, educational level and the starting capital of the roadside marketers were found to be significant at 5% (P<0.05) and had the expected signs while the coefficients of the total sales, purchase cost and consumer price were significant at 1% (P<0.01) level of probability and also had the expected signs. Roadside marketing is profitable, according to the study's findings, and it is advised that this strategy be investigated and updated by the Nigerian policymakers.