A rear sheet adjustment assembly of neck collar is provided, including a nape base and a support sheet. The nape base includes a main body, at least one stopper, a positioning member and a plurality of openings. The at least one stopper is connected with the main body and defines an inserting space therebetween. The positioning member is disposed on the main body. The positioning member has a first combination portion. The support sheet is adapted for supporting a nape of a neck and movably inserted within the inserting space. The support sheet has a plurality of second combination portions, and each of the second combination portions is adjustably engageable with the first combination portion.