Is it foggy in dec in beijing? Like at the great wall and other popular attraction.

Yes, it may be foggy in BJ city in Dec. as well as in some attractions. In this month, the average tempeature shall be around -5C, so it will be cold and winter clothes are needed.

Thank you for your reply. How bad is the fog? Do you have some pictures to share? I am quite worried about the fog. I am going with a group tour and the guide claim that it will not be foggy because it is dry winter. Am I able to take pictures and see anything?

The fog will not be so bad, so it is no needed to worry about it. It is still suggested to keep attention on the weather forecast before your trip.