Currently, automated driving vehicles perform the function of assisting driving at the level of Level 2, and the driver must always be careful to look forward and perform steering and pedal operations, just like existing non-autonomous cars. However, in Level 4 highly automated vehicles (HAV), there is no driver intervention, so passengers can take various postures and actions. In this situation, in order to secure the collision safety of autonomous vehicles, it is necessary to reflect various conditions of passengers. To this end, this study conducted a study on the preferred seating position and seating posture under autonomous vehicle conditions. An online survey was conducted on 80 expert groups with knowledge of self-driving cars, including demographics, driving-related questions, seating-related questions in sedans, seating-related questions in MPVs, and common questions. A total of 16 items were conducted. Through this, preferred seating positions and sitting postures for each major activity were collected. Seat rotation was the preferred sitting posture when talking with a passenger, and seat back relaxation was confirmed as the preferred sitting posture under sleeping conditions. In addition, the rate of negative opinions (safety concerns, anxiety, and motion sickness concerns) about the seat rotation function was high at 92% through common questions. Negative opinions (safety concerns, poor space utilization, high cost) about the relaxation seat were 77%. In the above survey results, it was found that respondents considered convenience (56%) more important than safety (44%). Through this study, it was possible to identify the preferred seating position and posture of passengers under autonomous vehicle conditions, and this is expected to be useful data that can be used for testing and verification necessary to secure integrated safety in the future.