Current smart phone carriers are sharing the same interface icon style, which is materialized drawing with filtered details. However “complex details can become confusing and may appear muddy at smaller sizes” (iOS human interface design guidelines, 2015). Therefore, The central aim of this study is to examine to what point viewers can recognize or feel lost in recognizing smart phone interface icons, in terms of simplicity levels. Then interface designers can design and produce simplified smart phone interface icons to save space on screens and make icons more clear at small sizes. This study included three survey parts to test the icon recognition of differently simplified icons. There were two phases in this study: in Phase 1, participants were asked to check all icons of five simplicity levels that they can recognize as the meaning of the label in each question's stem. From the results of Phase 1, the most recognizable simplicity level of icons and simplest level of icons that participants could recognize were selected for Phase 2. Lastly, the researcher compared the icon recognition rates between the icons of these two simplicity levels. The results indicated that the extremely simplified icons had similar correct icon recognition rates as those of the relatively more detailed icons, and participants' personal backgrounds (age, gender, educational background, first language, and currently used phone brand) affected the icon recognition.