This thesis focuses on Myanmar and Cambodia’s relations with China. Both countries used to be China’s“most trusted supporters”in Southeast Asia. However since Myanmar’s civil reforms in 2011 a rift has appeared between China and Myanmar. Cambodia’s relations with China，on the other hand remain close. This research will inquire into the factors that caused this discrepancy in this country’s position towards China. Realism，in combination with domestic politics theories will be used as theoretical framework to analyse this puzzle. This paper will argue that Cambodia and Myanmar’s different engagement with Western countries is a key explanatory factor. Up to its reforms Myanmar endured diplomatic isolation and sanctions from the West. On the other hand Western countries continued their relations with Cambodia，moreover they continue to provide a lot of aid to the Cambodian regime. This created a very different relationship with China，in the case of Myanmar it was a relationship based on necessity，whereas Cambodia’s relations with China are based on opportunity. The second main argument this paper will advance is that Cambodia’s historic enmity with Vietnam reduces anti-Chinese sentiment in Cambodia and therefore encourages a better relationship between China and Cambodia.