Farm-size is of an extreme interest in agriculture. This has been much debated over what may be appropriate size of the farm because the size of the operating unit, as in the case of manufacturing industries, decisively affects the income from agriculture. Since the amount of income is dependent on the size of the farm, preponderance in small and tiny holdings is mainly responsible poor peasantry in the third world countries. Even where there is no cost advantage or disadvantage for farms of various sizes, small farms will have, under usual price relationship, lower incomes and savings than large farms. Thus, size of farms is a vital element in determining the earning capacity of the farmer as well as the efficiency of a farming unit. Hence the present study aims to analyse the resource use efficiency of input factors in different size-level farms based on entire sample of Farms in three revenue mandals of Nellore District, Andhra Pradesh. Data was collected for the variables with the help of survey method through personal interviews of the farmers selected through mixed sampling. By studying the Marginal Value Products of factors of production, we assessed the relative importance of factors of production.