The telecommunication industry nowadays has grown rapidly in line with high awareness of job satisfaction towards employees. In this context, the importance of factors effecting job satisfaction will affect the sustainability of main-company Telecom and to be competitive in business Telecommunication Industry. The aims of this study to examine the level of job satisfaction, the relationship between factors effecting employees and job satisfaction, and to know the most important factor that influence job satisfactions towards main-company Telecom. The study adopted survey approach to collect 113 usable respondents from staff in 3 main-company Telecom (Elabram Systems, OCK and Southpac) based on purposive sampling method. Therefore, validity and reliability of the instruments were examined through panel of expert and also the small sample of the data was analyzed using SPSS. This study reminds that there are five possible factors (relationship with co-worker, salary, job security, work life balance and working environment) that influencing job satisfaction towards main-company Telecom in Klang Valley. Future research could advance this study by extended to other region main-company Telecom or make a comparison in between of regions to get better understanding of the factors that influence job satisfaction towards main-company Telecom industry.