The article aims to identify the determinants of short- and long-term corporate financial investment in Poland, with a particular emphasis on the saving and interest rates. We conducted the analysis based on unbalanced panel data for companies with at least 10 employees from the Polish Central Statistical Office’s GUS F-02 annual reports for 1995–2012. We used the system GMM estimator (Generalized Method of Moments; Arellano, Bover 1995; Blundell, Bond 1998) to estimate the parameters, and we applied a robust variance-covariance matrix. The research findings show a significant negative correlation between financial investments and cash flow, which means that liquidity problems in the core business induce companies to increase long-term financial investments (securities) as a precautionary motive. By contrast, the accumulation of surplus cash from operating activities in the form of savings increases long-term financial investments. The research also points to a positive impact of the real interbank overnight interest rate. This means that higher interest rates increase the opportunity cost of investments in fixed capital and may encourage companies to spend their savings on buying financial assets (interest rate channel of monetary policy) instead of investing in fixed capital or research and development (R&D).