|Currently, this feature is not possible in Salesforce1, both when in the Salesforce1 app and when accessing Salesforce1 on a supported mobile browser. The Case Comments Related List in Salesforce1 allows Users to view existing Case Comments. To add Case Comments, please use the desktop version of Salesforce. As an alternative, a custom action can be created with Visualforce that allows for this functionality. However, we do not provide the code for this. There are many online resources that explain how to achieve this.