This study examines whether government spending in the Nigerian Agricultural sector has been consistent with Wagner' Law. To test the validity of Wagner's law, six alternative functional forms were adopted, using annual data from the Nigerian agricultural sector over the time period 1961 - 2012. Data was analyzed using cointegration and granger causality test. The result of the Johansen and Juselius cointegration test showed the existence of a long run relationship between various items of agricultural capital expenditure as well as agricultural contribution to Gross Domestic Product. The granger causality test result confirmed that Wagner's law holds in the Nigerian agricultural sector. However, there was no clear evidence of government spending causing national income. Hence, the Keynesian proposition of government spending as a policy instrument that encourage and lead growth in the sector is not supported by the data used.