Thailand's economic base was gradually shifted from agricultural-based to industrial and service country for the last 30 years. The purpose of this study was to investigate the effect of those structural changes on economic performance using Cochrane - Orcutt and Newey-West Model. For the result, an incremental employment in agricultural sector yielded the negative effect on economy. Also, an increase in employment in service sector was better than industrial sector in supporting economic growth. Thus, government of Thailand should no longer support agricultural sector but service-based economy instead.