With the advantages of high popularity, convenient operation, open-source operation systems, high resolution imaging, and excellent computing capabilities, smartphones have been widely used as the core of detection system for calculation, control, and real-time display. Hence, smartphones play an important role in electrochemical detection and optical detection. Smartphone-based electrochemical systems were combined with screen-printed electrode and interdigital electrodes for in situ detection. The electrodes were modified with biomaterials, chemical materials, and nanomaterials for biosensors and biodetection, such as 3-amino phenylboronic acid nanocomposites, graphene, gold nanoparticles, zinc oxide nanoparticles, carbon nanotubes, proteins, peptides, and antibodies. With the modified electrodes, the smartphone-based impedance system was used to detect acetone, bovine serum albumin, human serum albumin, and trinitrotoluene, while smartphone-based amperometric system was employed to monitor glucose, ascorbic acid, dopamine, uric acid, and levodopa. The smartphone-based electrochemical system for biosensors and biodetection has provided miniaturized and portable alternative for diagnosis, which is promising to find application in point-of-care testing (POCT).