Extracting meaningful and valuable knowledge from databases is often done by various data mining algorithms. Nowadays, databases are distributed among two or more parties because of different reasons such as physical and geographical restrictions and the most important issue is privacy. Related data is normally maintained by more than one organization, each of which wants to keep its individual information private. Thus, privacy-preserving techniques and protocols are designed to perform data mining on distributed environments when privacy is highly concerned. Cluster analysis is a technique in data mining, by which data can be divided into some meaningful clusters, and it has an important role in different fields such as bio-informatics, marketing, machine learning, climate and medicine, k-means Clustering is a prominent algorithm in this category which creates a one-level clustering of data. In this paper we introduce privacy-preserving protocols for this algorithm, along with a protocol for Secure comparison, known as the Millionaires' Problem, as a sub-protocol, to handle the clustering of horizontally or vertically partitioned data among two or more parties.