Analysis and design of programs by using tools has emerged to a standard technique in object-oriented software engineering. Many of these tools claim to implement methods according to the UML standard and some of the tools provide automatic layout of the diagrams drawn by the user or generated automatically from source code. In this paper we propose a set of aesthetic criteria for UML class diagrams and discuss the relation between these criteria, HCI and design aspects of object-oriented software. First we describe critics from the viewpoint of HCI to the UML notation and restrict ourself to changes which do not require nonstandard modifications to the UML notation guide, then we list quality relations between class diagrams and object-oriented software models. After that our set of aesthetic criteria, that reflect the highly sophisticated structural and semantic features of UML class diagrams, is explained. Finally, we show that an implementation and measurement of this proposal i...