This paper examines the role of R&D spending on economic growth of developing economies between the periods of 2000 and 2009. The impact of R&D spending on these economies is determined by using dynamic system GMM, pooled mean group and three stage least square-GMM models. Sixty-six countries are studied and further grouped as; upper-middle-income economies and lower middle-income economies. The result reveals a beneficial impact of R&D spending on economic growth in developing countries. The effect of R&D spending on growth is positive for upper middle-income economies while insignificant in lower income economies. R&D spending has different short and long run effects on growth. Using simultaneous equation models to account for simultaneity and endogeneity, R&D spending remains beneficial to growth and the results remain consistent with the dynamic system estimator.