Negative self-thought is associated with the deterioration of many mental health issues, such as depression, anxiety, self-esteem, and social isolation. Due to the impact negative thinking about oneself has on many individuals, there is a need for an accessible and cost-effective intervention. Cognitive Behavioural Therapy (CBT) focuses on insight and recognising the connection between thoughts, feelings, and behaviours surrounding an event. Acceptance and Commitment Therapy (ACT) focuses on being in the moment and accepting all thoughts that come up. In this study, I used a single-subject single-treatment design (A-B-A or A-C-A) to compare the effectiveness of two iHealth applications; iCBT™ and ACT Companion™ application in reducing negative thinking about oneself. Both approaches significantly reduced the mean daily negative thinking about oneself, however, the ACT Companion™ app was overall more effective. I found a significant increase in mean psychological flexibility, and the need for self-reflection and insight. Overall, both applications are promising forms of treatment for individuals struggling with some level of negative thinking about oneself. Overall, the ACT Companion™ application has shown to be an effective way of reducing negative thinking about oneself, in a relatively short period of time, and at the user’s own discretion.