Does taxation structure have an impact on investment dynamics? In our paper we evaluate the share of tax revenues in GDP and investment outcomes, making use of gross fixed capital formation as a proxy for investment. This empirical analysis is carried out for all OECD countries, during the period of 1980-2015, to assess the tax system composition effects in both the short and the long-run. Resorting to panel data econometric techniques, the paper also aims to find optimal tax-investment threshold values. Our results lead us to conclude that there is a maximising effect of income taxation on investment growth when revenues from this tax source are about 10.7%. Furthermore, we find that revenues from social security contributions are detrimental to growth, in both the short and the long-run, while tax revenues from firms and consumption are only detrimental in the short-run.