The fact that the musical oeuvre of Antun Dobronić has remained mainly unpublished suggested itself as a purpose of this doctoral thesis to examine his unknown and unpublished works in the field of music for piano and chamber music with piano in the first place. Only some of these works have been published, whereas the majority of them have not been performed ever since Dobronić's death. The selected compositions, presented and analysed in the thesis, have also been transcribed with the aim to publish and perform them in future. An attempt has been made, after a considerable lapse of time, to evaluate their significance in relation to the creative work of the other Croatian and European composers of the day. Since Dobronić's personality was always intriguing in his versatility, unwillingness to compromise and great working energy, several musicologists investigated various segments of his output and activity. However, his piano compositions and chamber music with piano have not been systematically examined until now and still exist only as manuscripts. Despite all well-meant attempts to understand Dobronić's works, he still seems to be an unknown, just like the bulk of his oeuvre. Within his exceedingly large musical legacy, the PhD candidate has chosen a segment that is closely connected to her profession, hoping that she could make the biggest contribution possible precisely in this field. Among all the examined musical pieces for piano and chamber music with piano, respectively, those have been analysed that had never been performed after Dobronić's death. Among the piano compositions, the most important are three piano cycles dedicated to Dobronić's children Lelja, Rajka and Draško, as well as the piano cycle From the Children's School World. Both cycles are quite untypical. They are not based on the ties with folk creation and present Dobronić in a completely different light. In spite of their anti-romantic traits, they show Dobronić as a lyricist who, departing from all traditional artistic procedures, presents his inner experience and his state of mind very realistically in his own way. The miniatures display all the elements of early music expressionism and, as such, deserve special attention. The analysed chamber music compositions with piano are also those that have not been performed ever since Dobronić's death. Among them, there are the Bosnian Rhapsody and the Piano Trio, and the Dubravka Suite for piano four-hands. Here, Dobronić remains faithful to his life-long pursuit to integrate folk creation into his works and lift them to a higher artistic level. Folk themes and motifs are revived in these compositions in a very special way. These works can also be regarded as expressionistic because all of them penetrate their psychological background of the contents and faithfully convey it. However, considering their original connectedness with folk music, in terms of style it would be more accurate to describe them as folk music expressionism. As such, they have a place in the context of music history and can worthily represent their author, as well as the works of Croatian composers.