Main objective of this study was to find out if uncertainty of operational cost of manufacturing firm in Kenya affects financial performance. Kenya manufacturing firms have not been performing as expected. They are to contribute to economic growth through GDP increment, market share, attract largest strategic investments in Key processing industry, increase sales locally and international, and employ 20% of Kenya Population. However, the manufacturing firms have been facing various financial and non-financial challenges. Average contribution to GDP has staggered at 10%, reported declining profit and sales, and some firms have moved out of market. Many factors have been cited to be contributing to declining financial performance. However, the influence of operational cost uncertainty on financial performance of manufacturing firms in Kenya is not conclusive. Hence, necessitating the current study to examine the influence of firm operational cost uncertainty on financial performance of manufacturing firms in Kenya. The study anchored its variable on agency theory. Indicators of operational cost uncertainty were Labor cost ratio and research and development ratio, and proxy of performance were ROS and ROE. The study adopted positivism Philosophy and correlation design. Target population was 856 manufacturing firms registered with KAM. A sample of 90 firms was selected using Stratified random sampling technique for 14 sectors and each sample picked by random sampling. The study covered 12 years starting from 2009 to 2020. Panel data was collected from audited financial statements using data collection instrument. Diagnostic tests were carried out to test assumption of linear regression and data analyzed using E-view 11.8. Results showed that operational cost uncertainty had positive and significant influence on financial performance of manufacturing firms in Kenya. The study recommends having enhanced research and development in place that will take advantage of market niche for products and technology for production.