Nowadays, plastic made from oil and oil derivatives is one of the most used materials in people's daily lives. However, due to its increasing production, a problem of its toxicity, adequate disposal and accumulation in the environment is arising. For this reason, scientific research is aimed towards new types of biodegradable plastics in order to replace the synthetic ones. One of the biodegradable types are polyhydroxyalkanoates, PHA. PHAs are specific because of their synthesis method and their completely biodegradable nature. They can only be produced by metabolic processes of microorganisms. If microorganisms are provided with a substrate with nitrogen deficiency and a large excess of carbon, the microorganisms will start producing PHA as a reserve energy source. Recently, agro-industrial waste has been considered as a potential substrate that could be used for these purposes. By using agro-industrial waste to produce PHA, the amount of waste itself would be reduced, and at the same time a new and sustainable material would be produced. Such process could potentially be implemented in industrial infrastructure, which could meet the requirements of the circular economy, whilst at the same time have a favorable impact on the environment. However, agro-industrial waste requires adequate pretreatment in order to become a favorable substrate for PHA production. In this paper, an ultrasound pretreatment of waste starch was examined by changing three factors, the time of ultrasonic treatment, the ultrasonic power and the concentration of the NaOH solution. Four bacteria were isolated from starch: Leukonostoc sp., Citrobacter freundii, Staphilococcus lentus and Bacillus licheniformis and three fungi: Cryptococcus humicola, Geotrichum klebahnii and Candida krusei. All of them can produce PHA. The same microorganisms were used in the solid-state fermentation process, SSF, to produce PHA. The results showed values of PHA accumulation not higher than 1%, among which the highest value was 0,5572% under starch pretreatment conditions of 30 minutes, 2 W mL^-1 and 0,01 mol L^-1. In general, results have shown that stronger starch pretreatment conditions (longer pretreatment, higher ultrasound power and higher concentration of NaOH solution) result with lower PHA accumulation. Fourier transformation infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA) showed that synthesized PHA polymers could potentially be PHB and PHV homopolymers, PHBV copolymers with different HB and HV proportions or copolymers made of various short-chain-length and medium-chain-length PHAs.