A buffer device for small-sized roller shade comprises a housing body, a covered cylinder within the housing body, an oil seal over the outer edge of the covered cylinder and sealing with respect to the housing body, a covering body secured onto the housing body, a spring surrounding the outer edge of the covered cylinder away from the housing body and the covering body, a rotating body accommodating the covered cylinder around which the spring is provided, such that the spring and the covered cylinder are combined to rotate, a closure cap connected over the outer edge of the covered cylinder and synchronously rotated therewith, and a securing part away from the housing body while combined with the closure cap and the covered cylinder. Thus, the buffer device is reduced in volume for providing a shade panel with buffer effect in drawing/furling process.