This paper compared the retrieval effectiveness of the Google and Yahoo. Both precision and relative recall were considered for evaluating the effectiveness of the search engines. Queries using concepts in the field of library and information science were tested and were divided into one-word queries, simple multi-word queries and complex multi-word queries. Results of the study showed that the precision of Google was high for simple multi-word queries (0.97) and Yahoo had comparatively high precision for complex multi-word queries (0.76). Relative recall of Google was high for simple one- word queries (0.92) while Yahoo had higher relative recall for complex multi-word queries (0.61).