Digital money laundering, as one of the emerging challenges in contemporary financial systems, has disrupted the traditional structure of private transactions and the legal rules governing the validity of contracts. The main issue of this study is to examine the effects of illicit proceeds derived from digital assets on the legal validity of transactions, as well as to analyze legislative and enforcement challenges within the Iranian legal system and selected comparative jurisdictions. The research method is descriptive–analytical, based on library sources, academic articles, and domestic and international legal documents to examine different dimensions of the subject. The objectives include explaining the mechanisms of digital money laundering, analyzing its impact on contract validity, identifying legislative gaps, and proposing legal solutions to reduce its negative consequences. The findings indicate that the decentralized and cross-border nature of digital assets makes tracing and proving the origin of funds difficult, thereby increasing legal risk in private transactions and weakening contractual legal certainty. It is also shown that existing Iranian laws are not fully aligned with financial technology realities, and deficiencies exist in evidence rules, intermediary liability, and supervisory infrastructures. In contrast, some legal systems have achieved greater effectiveness in controlling this phenomenon through transparency mechanisms, customer identification rules, and cross-border cooperation. Therefore, effective countermeasures against digital money laundering require legislative reform, institutional strengthening, and the use of technological tools.