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Presently in Nigeria, a large proportion of the population depends on imported rice as locally made rice are not produced in large quantity that can feed the whole populace. The fragmentation index of the study area is 0.86 which means that rice farmers in Osun State operate on many scattered plots and they have an average farm size of only 0.53 hectares. Multi stage sampling technique was used in selecting respondents for the study. Simple random sampling was used to select rice farmers through there association in each of their local government areas. A hundred and fifty-three respondents were used.  Data were collected with the means of well-structured questionnaire. Data were analyzed using descriptive statistics, Ordinary Least Square (OLS) Model, Net Margin Analysis and the Cobb-Douglas Production function. This study reveals that years of education(-0.0063731), average plot size(-0.0729282) and distance of plots to homestead(-0.1432701) have significant effect on land fragmentation among rice farmers in Osun State while other variables such as sex(0.611602), age(0.000867), years of farming(-0.0016231),household size(0.0098885), average distance between plots(0.0457988) and access to extension services(-0.0310289) do not have a significant effect on land fragmentation among rice farmers in the study area. This study further revealed that land fragmentation (20.1697), labour cost (0.0002481), quantity of seed (0.0943123) and fertilizer used (0.3799082) has a positive and significant effect on the productivity of rice farmers in the study area whereas other variables like the average distance between plots, average distance between plots and homestead, years of farming and the level of education of the rice farmers has no effect on their productivity. Land fragmentation has a great influence on the productivity of rice farmers in Osun State. It was recommended that the farmers should use improved variety of seeds and not the local varieties to increase their production as the government creates more awareness on rice production by organizing seminars and workshops for the unemployed youths and encouraging them to go into rice production.   
Key words: Cobb-Douglas Production function, Land Fragmentation, Net Margin Analysis, Productivity