The aim of this research was to examine the relationship between life satisfaction, mobile phone usage time, and different mobile phone activities in early adolescence. The Brief Multidimensional Students’ Life Satisfaction Scale (BMSLSS; Seligson et al., 2003) was used to measure life satisfaction. A Mobile Phone Activity Scale was developed to examine various activities on mobile phones or smartphones. A graphic timeline of mobile phone usage was used to measure the amount of time spent on mobile phones. The sample consisted of 282 children (168 girls). The data used in this study were obtained from a research project conducted within the framework of the HRZZ UIP project “Digital technology in the family: patterns of behavior and effects on child development”. The results show that children often use their mobile phones to communicate, sometimes to access social networks, and to search for information. Girls more often than boys use their mobile phones for communication and social networking activities. The age of children is positively associated with the use of mobile phones for social networks and searching for information, as well as with the time spent on mobile phones. Using mobile phones to search for information is a positive predictor of global life satisfaction and family satisfaction. The use of mobile phones for social networks is a negative predictor of general life satisfaction and satisfaction with the place of life.