Since the attainment of independence in 1960, it has been known that party polities has not really done much in the area of national integration in Nigeria because of this; political parties in Nigeria tend to promote ethnic and private interest which has milted against National integration. Based on this, this study sought to investigate the party politics and national integration with a view to analyzing the nature and structure of the People ’s Democratic Parties (PDP) between 1999 – 2015 in order to ascertain how it has promoted National Integration in Nigeria. Qualitative method of data collection based on documentary evidence was used. Secondary source of data was employed. Also Qualitative descriptive method based on content analysis was used as our method of analysis. The work was predicated on the systems theory approach as our theoretical framework of analysis, this study desire to investigate the extent to which fourth republic parties’ politic has impacted on national integration. The study found that the structures of parties in fourth republics tended to promote ethnic and private interest and this really affected national integration. The Nigerian ruling class, patriotism or national interest was a hollow propaganda intended to mask class selfishness. The ruling class demonstrated their private interest through awarding contracts to party loyalists who abandon those contracts and embezzle the money and nothing would be done. It had been noted that parties politics have not really done much on the achievement of national integration, we recommended amongst others things that Political parties in Nigeria should be formed on the basis of promoting National integration. Grassroots and people oriented political parties should be formed, founding of political parties should not be done by few wealthy individuals but by the entire people. Also participation in political party activities should be open and transparent for all citizens.