Purpose The purpose of this paper is to find Batak Toba society's local wisdom of mutual cooperation in Toba Lake area: a linguistic anthropology study. Design/methodology/approach This research employed qualitative paradigm. As a qualitative research, it employed four methods of data collection, namely in-depth open-ended interview, direct participatory observation, focus group discussion which is often abbreviated as FGD, and written documents. In-depth and open-ended interviews were applied to obtain data from the informants who understand the local wisdom of mutual cooperation, the traditional expressions as the collective memory of mutual cooperation, and the terms of mutual cooperation in Batak Toba society. Findings Based on the research findings, Batak Toba society has terms for gotong royong (mutual cooperation). They are marsirimpa or marsirumpa (cohesive, in unison, and together). It means that the basic rule of gotong royong (mutual cooperation) in Batak Toba society is the cohesion, synchrony, and togetherness. In other words, gotong royong (mutual cooperation) in Batak Toba society is working cohesively, in unison, and together, which is practiced in the life cycles, livelihood cycles, and public works. Originality/value This paper presents a new and significant contribution to the social and economic activity, especially socio-anthropology. People do not consider the implementation of mutual cooperation anymore. They forget that marsirimpa (the local term for mutual cooperation) can be used as a non-material capital to improve the socio-economic development. Marsirimpa can improve the social activity because its main principles are based on the solidarity and harmony. This research gives contribution economically to the people in the research area (Tippang village) compared to the neighboring area (Bakkara village). People in Tippang village get better income because they believe that many works, for instances, irrigating, paddy planting, until paddy cutting should be done together; they do not need to spend money for workers. Each clan has its own representative to manage irrigation. The activities of land digging and paddy cutting are collectively done. In relation to social anthropology, the tradition around the research area is still maintained because it makes people value the social interaction.
