The aim of this thesis is to test the possibility of using the DTLS security protocol with the MQTT communication protocol on Wireless Sensor Network (WSN). Both protocols have been developed long before the inspiration of the Internet of Things (IoT). Because their original purpose is compatible with implementing the IoT many are trying modifying them so they can be used in developing IoT applications based on the Contiki OS. First thing before testing the two protocols is very important, it requires to create the environment where all simulations will be executed with the intention of exploring the protocols. Also, if or how they can be combined. Next step involved running and testing of the MQTT protocol with intention of identifying how applications which includes this protocol work. Last step was to modify the tinyDTLS protocol created for tinyOS to work with the Contiki OS and to develop a client/server application to test the protocol. After experimenting with the two protocols has shown that both protocols are important for the IoT development and can later be used to accomplish many goals related to stable and secure communication. However, there are some compatibility issues related to the structure of the two protocol that have to be resolved before combining them together successfully.