Objective- In the context of finance theory, predicting the return / price or movements of financial assets over the historic data provides elemination of the uncertainty and make such assets manageable. Therefore, modeling the financial asset behaviors with objective and scientific methods greatly contribute to reduce and manage the risk. In this study, the direction of the relationship between the Gold prices and the BIST 100 index was determined and tried to be estimated within a certain probability  and how the change in the Gold prices in the Bayes Theorem would be reflected in the BIST 100 index. Methodology- Variables used in the study are the bullion gold gram sale price and BIST 100 index and the monthly closing prices of the mentioned variables are used as data set for the 18 years (2000: 01-2017: 07) period. The data were compiled from the official website of the Central Bank of the Republic of Turkey. E-Views 9 SV program was used for statistical analysis of data. During the methodological process, statistical methods such as Pearson Correlation Analysis and Bayes Theorem were used.  Findings- In the study, it was found that positive correlation (0,91) exist between these two financial assets. In addition, the significance of the correlation coefficient at the 5% significance level was tested and it was determined that there was a significant correlation between the Gold prices and the BIST 100 index.  At a later stage, it was tried to estimate with certain probability, how the BIST 100 index would react to an increase in gold prices. As a result of the analysis carried out in the framework of the Bayes theorem, it is found that increase of the gold prices will also lead to increase the BIST 100 index with  52.1%  probability.  Conclusion- It is important, valuable and necessary for investors to make accurate and on-the-spot decisions, especially in uncertainty and risk environment in the markets. If this uncertainty is managed by being reduced to a measurable risk level, it offers the opportunity to provide extraordinary returns or to minimize losses for individual and / or institutional investors. Working with scientific data and methods to understand, mitigate and manage the future risks of assets in this framework makes a significant contribution to the success of risk management strategies implemented by financial institutions. In this context, a positively and statistically significant relationship was found between gold price and BIST 100 index in the study. Moreover, in the case of an increase in gold prices, the BIST 100 index will increase too with 52.1% probability.