The objective of social networks is to promote knowledge through providing connections among individuals and forming social capital. The aims of this study are: i. to acknowledge the type of knowledge communicated Library and Information Science Through Discussion Group (LISDG), and ii. to investigate the extent to which the LISDG is capable to establish social capital. To fulfill the first aim, content analysis was used to analyze 1400 messages sent to LISDG. Findings show that although most of the messages sent to the LISDG (about 82%) are of the “Know-What” type of knowledge, the numbers of “Know-Why”, “Know-How” and “Know-Who” types have increased during the two year period of study. Survey study and questionnaire were used to fulfill the second aim of the study. Results indicate that LISDG has required characteristics such as trust, reciprocity, social support, suitable environment, commitment, cooperation and efficacy for being regarded as a social capital.