Cognitive processing biases to health-related information have been endorsed to be present in patients who are su ering from medical diseases. Attentional bias is one of the cognitive processes which facilitates the detection of health-threatening information. Interpretation bias is the other cognitive mechanism that makes patients attribute catastrophic meanings to ambiguous bodily sensations. Despite the literature demonstrating that attentional and interpretation biases increase negative emotions and challenge patients for adaptation to their health condition, the link between these two biases has remained unclear. While some theories claim that attentional and interpretation biases are interrelated, some state that they might be orthogonal components of cognitive processing. Therefore, this thesis aimed to investigate the relationship between interpretation and attentional biases to health-related information by modifying interpretation bias and studying its e ect on attentional bias. One hundred undergraduate students who lacked any medical or psychological problems were randomly allocated to Main-Modi cation or Placebo-Modi cation groups. All participants were asked to complete a battery of questionnaire including health anxiety inventory, Beck depression inventory, and Beck anxiety inventory in order to control between-group di erences regarding these constructs. As the pre-modi cation assessment, participants' interpretation and attentional biases to health-related information were respectively measured using the Modi ed Version of Online Interpretation Bias and Dot-probe tasks. Then, the Main- Modi cation group underwent Main On-line Negative Interpretation Bias Modi- cation Task aimed to impose unsafe and threatening interpretations for ambiguous health-related scenarios. The Placebo-modi cation group completed Placebo On-line Negative Interpretation Bias Modi cation Task. The modi cation phase was followed by post-modi cation measurements. Results revealed that the participants in the Main-Modi cation group experienced more post-test interpretation bias indexed by Unsafe valence of interpretations for ambiguous health-related situations compared to the Placebo group. The Post-test between-group di erence, however, was not signi cant for interpretation bias indexed by reaction time. Main negative interpretation bias modi cation succeeded to amplify attentional bias toward Ambiguous images in the Main group but Placebo modi cation did not do so. Unlike Placebo modi cation, Main modi cation increased attentional bias to Health-Related images as well. However, this increase was not statistically signi cant. These results can be considered as the pieces of evidence endorsing the idea that interpretation and attentional biases are interrelated aspects of cognitive processing. Repeated exposure to negative interpretations for health-related situations might increase patients' accessibility to negative meanings for interpreting further ambiguous health-related situations. In turn, the new negative meanings might facilitate detection of ambiguous bodily sensations or another health-related information known as attentional bias.