For de-interlacing a current interlaced field using a prior interlaced field and a subsequent interlaced field, a motion estimation method is performed with a group of motion-vector sets. Each motion-vector set includes at least two motion vectors. According to the two motion vectors and a specified block of the current interlaced field, which contains a missing pixel to be estimated, a pair of candidate blocks are defined in the prior and subsequent interlaced fields, respectively. By comparing a plurality of pairs of candidate blocks with the specified block, the best matching block pair can be found and used for de-interlacing.