Originally posted by JoeF
That depends on the country. Each country has different citizenship rules.
For example, some countries give citizenship to people who are married to a citizen of their country, regardless of where that person lives.
Of course, if residency in a country is required to get citizenship there, then it isn't possible for a US Permanent Resident to acquire that particular country's citizenship without losing Permanent Residency in the US. But that wasn't the question. Assuming that whatever is required to get citizenship of a particular country is already fulfilled, the act of acquiring that citizenship has no effect (positive or negative) on the GC.