Human　movement　dynamics　is　highly　correlated　with　stepping　locomotion.　This　paper　aims　to　explore　stepping　behavior　of　pedestrian　social　groups　on　stairs　through　a　field　observation.　A　total　of　96　singles　and　194　pedestrian　groups　with　different　sizes　were　adopted　as　test　subjects.　Their　stepping　features　such　as　speed,　step　length,　step　time　and　step　width　were　obtained　according　to　trajectory　extraction　and　curvature　calculation.　Relations　between　these　variables　during　ascending　and　descending　movement　on　stairs　are　analyzed　and　compared.　The　effects　of　group　sizes　and　movement　processes　on　stepping　locomotion　are　also　discussed.　It　is　discovered　that　both　step　time　and　step　width　for　groups　with　larger　size　are　significantly　higher　during　descending　movement.　This　study　provides　a　new　insight　into　stepping　behavior　of　pedestrian　groups　on　stairs,　and　is　beneficial　to　group　movement　modelling　and　pedestrian　facility　design.