The study investigated the effects of road transport infrastructure on agricultural sector development in Nigeria from 1985 to 2014, using secondary annual time series data on agricultural development (proxy by gross domestic product in the Agric sector) road transport infrastructure (proxy by length of paved road per square kilometer of area) export and capital, all obtained from the Central Bank of Nigeria (CBN) [3], and National Bureau of Statistics (NBS) [16], statistical bulletins. The data were analyzed using Granger Causality test and Ordinary Least Square estimation techniques. The study concluded that a positive and statistically significant relationship exists between road transport infrastructures (LRT) also evidence was found of a unidirectional causality from agricultural sector development to transport infrastructure. The study, therefore, recommends that adequate and timely maintenance of existing roads should be carried out as well as enacting appropriate regulations that ensure proper implementation and completion of new road construction contracts in the country in order to boost agricultural sector development, reduce wastage of farm produce and increase the possibility of economic diversification.