Kastamonu Halva has been produced with traditional methods by small enterprises for a long time. With the help of development seen in Turkish economy more people began to demand Kastamonu Halva. This increase in demand caused increase in production of Kastamonu Halva. In addition new firms began to produce Kastamonu Halva sector. According to economic literature, economic efficiency can be provided by competitive market structure. Our aim is to search market structure of Kastamonu Halva and changes of concentration ratio in Kastamonu Halva production by years. To this aim we conducted a query in producers in this sector and use these results in our analysis. We have reached remarkable results about this sector in our analysis. Concentration in Kastamonu Halva Production sector decreases with time. Before 2003, market shows oligopolistic characteristics and higher concentration. However then concentration ratios started to decrease and final market characteristics show lower concentration and higher competition. So, in the absence of barriers to entry market structure can change with time.