Background: The S Health application provides an estimate of the amount of physical activity by measuring the number of steps during activities. The purpose was to assess the accuracy of step-counting with different smartphones using the S Health step counting application at long and short walking distances, and stair climbing. Material and methods: 26 participants (aged 28.85 ± 4.85 years) conducted three tests: 20-step test, 60-step stair test, and 6-minute walk test. Three smartphones models of the latest generation and two models of an earlier one were assessed. The StepWatch pedometer was used as a criterion. Results: Only one phone of the latest generation produced the most consistent and accurate results as compared to the pedometer in the 60-step stair test and 6-minute walk test (r=0.840), while the correlation of the other four smartphones was weak, from r=0.257 to r=0.482. Generally, the accuracy increased with the increasing amount of steps in all devices and the mean absolute percentage error decreased. Errors ranged between 5.8 and 56.9% for the 20-step test, 1.9-22.4% for the 60-step stair test, and 1.1-17.8% for the 6-minute walk test. Conclusion: The results suggest that accuracy of smart-phones increase with increased number of steps and correspond to newer models.