Portable, low-cost smartphone platform microscopic systems have emerged as a potential tool for imaging of various micron and sub-micron scale particles in recent years [Ozcan, 2014; Pirnstill & Coté, 2015; Breslauer et al., 2009; Zhu et al., 2011]. In most of the reported works, it involves either the use of sophisticated optical set-ups along with a high-end computational tool for post-processing of the captured images, or it requires a high-end configured smartphone to obtain enhanced imaging of the sample. Present work reports the working of a low-cost, field-portable 520X optical microscope using a smartphone. The proposed smartphone microscopic system has been designed by attaching a 3D printed compact optical set-up to the rear camera of a regular smartphone. By using cloud-based services, an image processing algorithm has been developed which can be accessed anytime through a mobile broadband network. Using this facility, the quality of the captured images can be further enhanced, thus obviating the need for dedicated computational tools for post-processing of the images. With the designed microscopic system, an optical resolution ∼ 2 µm has been obtained. Upon post-processing, the resolution of the captured images can be improved further. It is envisioned that with properly designed optical set-up in 3D printer and by developing an image processing application in the cloud, it is possible to obtain a low-cost, user-friendly, field-portable optical microscope on a regular smartphone that performs at par with that of a laboratory-grade microscope. This article is protected by copyright. All rights reserved.