An organization’s ability to implement its strategy successfully is a result of its ability to overcome obstacles leading to poor strategy implementation. However, a myriad of factors can potentially affect the process by which strategic plans are turned into organizational action. This study sough to determine the factors influencing the implementation of strategic plans in small manufacturing firms in Nairobi County. Specifically, the study examined the effect of strategic innovation, strategic leadership and organizational culture on implementation of strategic plans in small manufacturing firms in Nairobi County. The study was informed by the Contingency theory. The study adopted a descriptive survey research. The study targeted 50 small manufacturing firms in Nairobi County. Purposive sampling was used to select a manager and supervisor in each of the small manufacturing firms. A sample size of 100 respondents was used. A multiple regression analysis was used to establish the relationship between institutional factors and the implementation of strategic plans. SPSS statistical software was used to analyze the data. The results indicated that strategic innovation and implementation of strategic plans in small manufacturing firms is positively and significantly related. Strategic leadership and implementation of strategic plans in small manufacturing firms is positively and significantly related. Lastly, results showed that organization culture and implementation of strategic plans in small manufacturing firms is positively and significantly related. The study concluded that strategic innovation, strategic leadership and organizational culture significantly influence implementation of strategic plans in small manufacturing firms. The study recommends that the small manufacturing firms’ should understand the role organization culture play in management of organizations. They should be in a position to build a culture that is aligned to the strategic plans that they adopt. The small manufacturing firms’ managers should also develop strategic leadership to coordinate all the other resources to attain the desired goals. Strategic leadership determines success or failure of a strategic plan. Key words: Strategic Innovation, Strategic Leadership and Organizational Culture, Strategic Plans & Small Manufacturing Firms