Introduction: Decision biases are one of the most important research areas in the field of entrepreneurs' decision-making, and researchers have considered a set of different individual, organizational and environmental factors to be effective in its formation and development, as well as the decision to establish a business, unprepared entry into new markets, the decision to produce Pioneer products as well as various business failures such as going out of business were identified as the most important positive and negative consequences of decision biases in entrepreneurs' decisions. Methodology: The present research has investigated the mediation of decision bias between design thinking on the development of small businesses located in Qazvin province, which is practical in terms of its purpose, and in terms of method, it is a descriptive and survey research. The statistical population of this research consists of 174 small business managers based in Qazvin province, using the Cochran sampling formula, the sample size is 91 managers who were selected based on simple random sampling and research information was collected based on a standard questionnaire. Data analysis was done through structural equations (SME) and PLS-SPSS4 software. Findings: According to the results obtained and the hypotheses of the research, the findings show that due to the positive standard coefficient, that there is a significant relationship between the two variables of design thinking on the bias of ease of recall, that the strength of the relationship between the variable of design thinking on increasing the bias of ease of recall is 0/724 has been calculated and according to the decision bias hypothesis, the relationship between design thinking on small business development due to the positive standard coefficient mediates between the variables and the strength of the relationship between the decision bias variable on the increase of design thinking on small business development 0/755-0/627 has been calculated, also according to the hypothesis of the research, it shows that the impact statistics of the test, which is greater than the critical value of the impact factor at the error level of 4%. Conclusion: From the current research, we can conclude that design thinking promotes the progress and development of small businesses and makes these businesses improve the quality of decisions and accelerate their organizational goals by recognizing biases.