This study analyzed the diversification strategy type and the causes for difference of diversification strategy type between Tencent and NHN. Tencent has grown as number one online portal in China by providing instant messenger(IM) service and for online game. NHH is also the biggest online portal in Korea while providing web search service. To do so, this study suggested four questions as follow; firstly, what are the main factors making Tencent a dominant online portal in China? Secondly, how the diversification strategy type of Tencent has changed recently and what is the driving force? Thirdly, how the diversification strategy type of NHN has changed and what is the driving force? Fourthly, what makes the difference of strategy type between Tencent and NHN? As the result, it turned out that the driving force of diversification strategy of Tencent resulted from its ‘One Stop’ service goal to cover diverse users as many as possible. However the synergy effect of NHN comes from the operational efficiency improvement rather than the financial collaboration among diverse online services. NHN also began to emphasize on the economy of scale rather than the economy of scope because the domestic market size of Korea is too small but the internal competition is more and more severe. Consequently it can be said that the diversification strategy type of NHN has been changed from the unrelated & domestic diversification to the related & international one. In contrast the synergy effect of Tencent turned out to be more close to the financial collaboration rather than to the operational efficiency, and Tencent more concentrates on the economy of scope than the economy of scale. Therefore it can argue that the diversification strategy type of Tencent has been changed from the related & domestic diversification to the unrelated & domestic one. Actually Tencent does not need to be hurry as much as NHN in going abroad but has to expand rapidly as many as various online service sectors due to the increase of new players in China. Furthermore this study tired to find out the causes for strategy difference between two firms through four factors’ approach of diamond model by M. Porter; demand condition, factor condition, supporting & relating industry condition, and strategy & rivalry structure condition.