Abstract: The purposes of the study are to examine, the relationship among the demographic factors affecting accidents at work, the causes or the personal, the policy and the environmental factors affecting accidents at work, the direct and indirect costs of accidents at work and to forecasts the accidents cost. The mixed method procedure was used to investigate the qualitative study by applying the purposive sampling technique. The subjects of the study were 61 employees who had accidents at work; thereby 41 employees were derived from 2 manufacturing companies and 20 employees from 5 construction projects of a construction company, of which the operation was from September 2015 to March 2016. The majority of participants are male (60.7%) with the average age of 37.95 years old and with level of education of grade 12 and above (50.8%); most of them are Thai employees (93.4%). Besides, the average working experience for manufacturing is at 15.60 years whereas that of construction is at 2.02 years. The participants had been provided with the safety training (70.5%) and most participants get severe accident (78.7%). The results further show that females were more likely to get severe accident 1.607 times than male. The participants without safety training were more likely to get severe accident 2.750 times than who had been provided with the safety training. The participants who graduated from grade 12 and above were more likely to get severe accident 8.395 times than those who graduated from grade 9 and under. Based on content analysis, the main factors of accidents were personal factors (70.00%), environmental factors (26.25%) and policy factors (3.75%), respectively. The costs of accidents at work were classified into 2 categories including the direct costs arising from the compensation and the medical treatment (22.22%) and the indirect costs arising from the accident compensation fund, the machine maintenance costs, the transportation costs, the accident management costs and the opportunity costs (77.78%).