Monetary policies are factors affecting aggregate demand and national production and income, and expansionary and contractionary policies can be distinguished, each of which has different economic effects on the economy. One of the variables that can be affected by monetary policies is the amount of corporate investment. In fact, tightening monetary policies increase the demand for money by increasing demand and national income, and as a result, the interest rate rises and leads to a decrease in investment. The main objective of this study is to examine the effect of monetary policies and the level of cash holdings on corporate investment in companies listed on the Tehran Stock Exchange. The statistical population consists of 105 companies, for the 5-year period 2019-2023, and the research model is estimated using the generalized method of moments (GMM). The results of the study showed that tightening monetary policies have a negative effect on corporate investment. The results also showed that cash holdings reduce the negative impact of tightening monetary policies on corporate investment. Our results provide clear evidence that cash holdings help Iranian businesses improve corporate investment efficiency by smoothing investment during periods of contractionary monetary policies. During periods of tighten monetary policies, the government and central bank can provide various government incentives or production subsidies to some disadvantaged companies or regions to maintain investment activities. Also, high cash reserves put managers in a position to make investment decisions independently of monetary policies.