Small business sector supports the Nigerian economy where it provides employment opportunity to most of its citizens. Despite its importance, most small businesses fail within the first five years notwithstanding the agencies established by Nigerian Government to support the sector. Most of the failure is due to numerous challenges facing the sector which borders of the success factors of small businesses. This paper identified the challenges based on the Lampadarious (2015) success factors framework to providing information for owners, managers, and researchers of small business success strategies. The paper identified fifteen critical challenges facing small businesses in Nigeria. The information will help owners and managers of small businesses to develop strategies to mitigate the challenges. Small business researchers will use the information to study challenges that are specific to the industry and investigate the strategies used by successful small businesses to mitigate the challenges. This paper might guide Nigerian government to develop policies that might reduce the external business environmental challenges of small businesses.