The study's primary purposes were to assess the sustainability index of hazelnut farms and explore the effects of part-time and full-time farming types on sustainability index in hazelnut production in the Giresun and Ordu Province of Turkey. One hundred fifty-two hazelnut farms were selected using the stratified sampling method, and data were collected. Several steps were taken, including using factor analysis after standardizing the variables to determine their weights to calculate the composite hazelnut farms sustainability index. The research findings showed that overall hazelnut sustainability scores of farms varied from 0.28 to 0.59, and the average score was 0.44 at sampled farms. The composite hazelnut sustainability index was at an unsatisfactory level. The social and economic sustainability index value of farms was equal, and they were higher than the environmental index value. The values were 0.50 and 0.30, respectively. While the economic sustainability index score of full-time farms was higher than that of part-time farms, and part-time farms had higher environmental sustainability index scores than that of full-time farms. Social sustainability scores were not different in terms of farm type. It was recommended that when designing and regulation support policies, policy-makers should differentiate part-time and full-time hazelnut farming. Training and extension programs must be planned to increase the level of knowledge of every willing farmer. In addition, training and certification programs must be implemented to enhance the quality of the foreign labor force.