In the study of inter-firm relations, the concept of transaction-specific investments has been regarded as an important factor. However, this study tried to draw an attention to the concept of relationship-specific investments. Specifically, this study focused on the factors determining the extent of relationship-specific investments between exporters and foreign buyers. Research results showed that the level of relationship-specific investments is determined mainly by such factors as product competitiveness, size of foreign buyers, competitive intensity of the focal foreign market, and years of business relationship. The findings indicate that the relationship-specific investments are determined not only by the logic of economics, namely future expected profits, but also by social relationships between firms.