This work reports a study to investigate and compare the coverage of Google Scholar, Citeseer in comparison with a traditional abstracting and indexing service (LISA) in library and information science. The research is motivated by an overview of the previous research, which found that there lacks systematic and comprehensive studies and comparisons in relation to the coverage of Google Scholar and conventional A&I databases for searching scholarly information or documents. it was found that no single search engine or database would cover all the relevant information. Choosing an appropriate search engine or database should consider different circumstances of searching topics and user demand scenarios. A combination of search engines and databases should be adopted to achieve comprehensive relevant information for a given topic.