Abstract. We present new optical photometry of open clusters NGC 2129, NGC1502 and King12 using data taken from the 104 cm Sampurnanand Telescope, Nainital. Our UBVRI CCD data reaches down to V∼21 mag, covers about twice the apparent size of the clusters and for King 12, it is presented for the first time. The archival near-infrared data from 2MASS is used to study the fundamental parameters and mass function of the clusters. Accurate structural parameters for the clusters are derived using radial density profiles while the evolutionary parameters are derived comparing colour-colour and colour-magnitude diagrams with the theoretical models. The mean reddening E(B-V) towards the cluster is found to be 0.73 mag, 0.69 mag and 0.62 mag. All the three clusters have ages of about 10 Myr; distances (in kpc) of 2.2, 0.96 and 3.02 respectively. The sizes of cluster lie in the range 1pc to 3.5 pc. Mass function for all the clusters are found to be consistent with the Salpeter value for Galactic field stars. Cluster NGC 2129 is found to be a typical case of an overlapping double open cluster.