This work has been done on the effect of investment, external aid on economic growth of Rwanda within a period of 2000 up to 2015. The general objective of this study was to analyze econometrically the effect of investment and external aid on economic growth in Rwanda This study contains the following specific objectives: To analyze the trends of investment, external aid and economic growth in Rwanda, to find the relationships between investment, external aid and economic growth in Rwanda. The following hypotheses have been formulated: The investment and external aid have the same tendency in Rwanda, the investment and external aid have the same effect on economic growth in Rwanda. To make the research richer and understandable, quantitative approach was used in forms of figures for statistical analysis, secondary data were collected from different reports and internet websites and analyzed using Eviews 7 and excel in order to provide enough and adequate information about economic growth, investment, external aids and economic growth in Rwanda also have been used in order to test research hypotheses. According to the results we found that the first and second hypotheses of this research were verified and confirmed as indicated in figure 4 & 5 and table 5, 8, 11 and 13 proved that investment and external aid have the same tendency and same effect. The variables were significantly fit the model as it was shown by the R2 Adjusted �higher than 80% which shows strong goodness of fit in the long-run and short run estimated model. As conclusion even if we face the problem of multicolinearity, it doesn�t affect the goodness of fit. But it cause one independent variable to switch the sign and became insignificant in other word it give a fake model as indicated in table 10 where external aid are affected in order to resolve this problem we remove one variable which is external aid and we still depend on investment. Investment has positive effect on economic growth in long-run and short run. Also investment and external aids are highly correlated as indicated in table 8 that is why they have same effect on economic growth. We recommend that the government of Rwanda should encourage the donors to change the form in which external aid comes which is in form of budget. Those external aids coming in form of budget are included in public investment that is why we face the problem of multicolinearty. Then donors might do this directly by supporting infrastructure, small farmers, building schools in order to resolve those problem and external aids have significant on economic growth.