This study examines the interrelation between foreign equity investments (FEIs) and the BIST 100 index, a pivotal indicator of the Turkish economy's overall performance. Given Turkey's emergence as a market with considerable potential returns, this analysis is particularly pertinent. The focus is on the volume of shares held by international investors in Borsa Istanbul and its impact on the BIST 100 index. Data spanning 924 weeks, from 2006 to 2023, form the empirical basis of this investigation. Stationarity of variables was assessed using the Augmented Dickey-Fuller (ADF) and Phillips-Peron (PP) unit root tests. The direction of causality between the studied variables was determined via a Granger causality test, employing a Vector Autoregressive (VAR) model. Findings reveal a bidirectional causality between the returns of the BIST 100 index and FEIs, aligning with prevailing hypotheses that posit a connection between foreign equity flows and stock market indices. This relationship underscores the integral role of international investments in shaping market dynamics within emerging economies. The study contributes to the understanding of financial market interdependencies, highlighting the significance of foreign investments in the context of a developing economy's stock market.