In order to take part in setting the ground for the Stara Zagora uprising of 1875, he returned to Rousse, and joined the preparations of a detachment's in Veliko Tarnovo.

The revolutionary committee in Giurgiu estimated Georgi Obretenov's training and sent him to the region of Sliven as a military instructor and as an assistant apostle to Ilarion Dragostinov.

Along with the weapons, Obretenov brought to Sliven some revolutionary proclamations, by-laws, a flag, and the inspiring poetry of Hristo Botev and Stefan Stambolov.

Then, he set off to the village of Korten to visit Georgi Kolev, the leader of the local revolutionary committee, with whose help he hid the items he carried in a wheat cart, and they both arrived in Sliven.

The military instructor, Georgi Obretenov, brought to Sliven modern guns, having issued directions about arms before departing from Giurgiu.