Mobile Crowd Sensing (MCS) has emerged as a powerful paradigm for large-scale data collection using sensor-enabled smartphones. However, existing MCS systems suffer from significant challenges such as lack of data quality assurance, privacy leakage, reliance on centralized authorities, and vulnerability to malicious users providing false data for incentives. To address these issues, this paper proposes a Blockchain-based Privacy-Preserving Quality Control (PPQC) mechanism for crowdsensing applications.The proposed system integrates blockchain technology to eliminate the need for a trusted central authority, ensuring data integrity, transparency, and secure reward distribution. A decentralized framework is designed where miners evaluate the quality of sensing data instead of a centralized server. To preserve user privacy, a node cooperation mechanism achieving k-anonymity is employed, along with homomorphic encryption techniques that allow computations on encrypted data without revealing sensitive information.Furthermore, a quality-based incentive mechanism is implemented, where rewards are assigned based on the accuracy of contributed data using noise estimation. The system also incorporates secure transaction mechanisms to prevent impersonation and fraudulent activities. Experimental results and performance analysis demonstrate that the proposed PPQC framework significantly improves data reliability, privacy protection, and system efficiency compared to existing approaches.Overall, the proposed solution provides a scalable, secure, and privacy-aware crowdsensing model suitable for real-world applications such as traffic monitoring, environmental sensing, and smart city services