To realize the implementation of agent based B2B e-commerce in ubiquitous environment, we design the b-cart based B2B agent framework. B-cart implies a buyer's shopping cart which a buyer carries. The prototype agent, named AgentU, is designed to provide an effective architecture for the direct purchasing from multiple external e-markets in ubiquitous environment. In this paper, by providing the features and architecture of AgentU, we analyze the pros and cons of this architecture with related issues such as comparison and inventory for B2B. The buyer using AgentU can collect items from different e-markets, and can order purchases simultaneously over the collected items. It also supports integrated services in personalized comparison on purchasing items, order tracking, financial/payment management, user's account management, negotiation management, personal decision support, tight integration between the b-cart and e-procurement systems, and context awareness.