Excessive and illegal exploitation of aquatic resources, especially Caspian sturgeon, are serious threats to their long term protection. Given the importance of maintaining stocks of sturgeon, the study on major causes of committing illegal fishing by fishermen is inevitable. In this study, data were collected through field-based surveys and a questionnaire. Validity and reliability of the questionnaire were assessed based on expert’s knowledge and Cronbach's alpha coefficient. Sample size was estimated using Cochran's formula, and then 201 questionnaires (designed based on Likert scale) were distributed among fishermen in Guilan province during spring and summer 2016 to answer questions related to social, economic, fisheries and conservation factors. Data were analyzed using Logit Model. Results showed that social and economic factors such as study level, income and job satisfaction had significant correlations with the occurrence of illegal fishing (P<0.05). Fishers who had less income and job satisfaction and lower study level were more likely to be involved in illegal fishing (P<0.05). In addition, fishermen with no license, giving less value for the protection of aquatic animals and who used non-standard fishing nets in deeper waters showed higher probability of committing illegal fishing. In conclusion, it appears that the probability of the occurrence of illegal fishing has a close association with a range of social, economic, fisheries and conservation parameters, and these findings could help fisheries managers in preventing the occurrence of illegal fishing activities.