Nigerian political parties in the Fourth Republic are characterized by a lack of internal democracy thus leading to the factionalization of some major political parties and the consequence defection of party members to other political parties to actualize their ambitions. This paper is attempts an analysis of the problem of internal democracy in both the ruling All Progressive Congress (APC) and the opposition People’s Democratic Party (PDP) to determine the extent to which each has succeeded or failed in this regard. It employed the theory of relative autonomy of the state and argues that the APC and the PDP authoritarianism intensified the challenge of internal democracy in Nigeria and that this authoritarian character of the ruling APC and the opposition PDP is a reflection of the authoritarian character of the Nigerian state. The paper is qualitative and utilizes the content analysis.It is discovered in this paper that the ruling APC did not fare better than the opposition PDP in terms of internal party democracy and concluded that this lack or absence of internal party democracy in Nigerian political parties generally does not only underminethe credibility of the electoral process but also makes the entire process undemocratic. This paper recommended among other things that the APC and the PDP leaders should adhere to internal democracy within their internal structures and dynamics especially in the selection of candidates for general elections which could be achieved by subordinating personal interests of party members to the larger interest of the political party. Keywords: Political Parties, Internal Party Democracy, APC, PDP, Internal Party crisis..