This study looks into how mergers affect operating effectiveness for merged companies in India's industrial industry in the post-merger phase. It particularly focuses on two important factors: employee perceptions of job security and employee satisfaction with organisational culture. The study has a cross-sectional design with a sample size of 250 people who were chosen through purposive sampling. It takes a quantitative approach. A standardised questionnaire with closed-ended questions based on Likert scales is used to collect the data. To compare the mean scores of perceived job security and organisational culture satisfaction before and after the merger, the obtained data is examined using paired t-tests. According to the data, employees' perceptions of job security significantly decreased in the post-merger period compared to the pre-merger period. Additionally, there has been a noticeable decrease in employee satisfaction with the organisational culture since the merger. The problems and worries that workers may have about their job security and organisational culture during the post-merger integration process are highlighted by these results. The study adds to the body of knowledge already available on mergers and how they affect operating efficiency in the manufacturing industry. The results highlight how crucial it is to have effective communication, transparency, and assistance during the merger process to reduce any negative effects on employees' perceptions of their job security and organisational culture. The study also recommends directions for further research, including as longitudinal analysis, qualitative research techniques, and comparisons across sectors and nations. Organisations may design strategies to improve post-merger integration and guarantee a seamless transition for employees by having a better understanding of the dynamics of mergers and their impact on employee experiences.