To meet the demand for low data rate, low power and cost-effective wireless communication IEEE 802.15.4 has grown its popularity. As it has low power it is potentially susceptible to interference by other wireless technologies with much higher power that also works in the same 2.4 GHz ISM band such as IEEE 802.11 standard, Bluetooth, and microwave. IEEE 802.11 standard operate random file transfer and wide deployment of Wi-Fi devices degrades the performance of IEEE 802.15.4 seriously. For WSN development strategy like changing channel, increasing transmission power and CSMA backoff, to act accordingly to the interference, information about the adjacency and impact of interference is necessary. The work reported aims at analyzing the performance of IEEE 802.15.4 under such kind of interferences. Firstly, the distance between the interferer and the WSN nodes is varied and the performance is analyzed. In the later part, the interference of the interferer is varied to analyze the impact of interference on communication. The results are compared and tell that how important is the proper design of networks for reliable communication of various technologies and to avoid degradation of the performance of IEEE 802.15.4.