The present study analyzes macroeconomic factors on the capital structure of companies by examining inflation rate, interest rate and gross domestic product. The present study is of an applied type in terms of its purpose. In terms of its inference method, this study is of a descriptive-analytical type. The research design is of a post-event type. The statistical population of this study is all petrochemical and oil processing companies listed on the Tehran Stock Exchange. In this study, the systematic elimination method is used for sampling. Data related to the research variables were extracted from the audited financial statements of companies listed on the Tehran Stock Exchange using the new Rahavard software and referring to sites related to the financial reports of companies such as the Kodal site. Descriptive and inferential statistical methods were used to analyze the research data. The results of the study indicate that none of the research hypotheses have been approved. Thus, the results obtained from the test of the first hypothesis, which examined the effect of uncertainty in the inflation rate on the capital structure of companies, show that the effect of uncertainty in the inflation rate on the capital structure of companies is not significant and at the 0.05 error level, the results did not lead to confirmation of the hypothesis.