In 1861, Rossier was in Siam, where he assisted the French zoologist Firmin Bocourt by taking ethnographic portraits for the latter's scientific expedition of 1861–1862, and in 1863, "Negretti and Zambra" issued a series of 30 stereographic portraits and landscapes taken in Siam that are almost certainly the work of Rossier. In February 1862, Rossier was again in Shanghai, where he sold his cameras and other photographic equipment before embarking for Europe. During his time in Asia it is possible that Rossier photographed in India; "Negretti and Zambra" issued a series of views of India at about the same time as Rossier's China views.