With the aim of developing an integrated health monitoring system, small piezoelectric Lamb wave transducers can be implemented into the structures to be monitored. Optimization of these transducers requires precise modeling of their radiation characteristics. In previous studies, bar-shaped integrated transducers have been modeled using a two-dimensional (2D) plane strain formulation. Thus prediction of the Lamb waves generated has been allowed. In this paper, additional information is provided by quantifying the in-plane directivity of such transducers. Prediction of the directivity pattern, as a function of the transducer length, is allowed by using a simple approximate model. Experimental measurements performed using various transducer lengths are in very good agreement with these theoretical predictions