Recently, many firms pursuing knowledge management both domestically and internationally have adopted and operated Communities of Practice (CoPs). This study aims to identify the factors influencing knowledge-sharing behavior among members in CoPs, thereby understanding the operating principles of CoPs and helping organizations pursuing knowledge management develop appropriate CoP operational strategies. Based on Triandis's model, a research model was exploratively constructed with perceived consequences, affect, social factors, and facilitating conditions as factors influencing knowledge sharing in CoPs. Perceived consequences were treated as a second-order factor, composed of anticipated recognition, anticipated reciprocal relationship, and anticipated usefulness. A survey was conducted with 179 respondents from an electronics company that operates CoPs voluntarily and informally in accordance with the definition of CoPs, and the data were analyzed using Partial Least Squares (PLS). The results are as follows: Perceived consequences, affect, social factors, and facilitating conditions all had significant effects on knowledge sharing in CoPs, confirming that Triandis's model is useful for explaining knowledge-sharing behavior in CoPs. Additionally, when the production group and R&D group were analyzed separately for significant influencing factors, perceived consequences and affect were significant for the R&D group, while social factors and facilitating conditions were significant for the production group. Organizations seeking successful CoP operations should understand that, as revealed in this study, cognitive, affective, social, and facilitating factors have a combined influence on knowledge sharing in CoPs, and should establish appropriate operational strategies and support systems accordingly. Furthermore, both researchers and practitioners should consider that the structure of influences on knowledge sharing may differ depending on the characteristics of the members constituting the CoPs.