Analysis of cell-cycle regulation, circadian rhythms, ovarian cycle, etc, demands finding periodicity in the biological data. In this work, we will consider gene expression data, which is usually quite noisy and comprise of small number of samples from very few periods (2 - 3). We propose a n on-parametric method for detecting the period and shape of the periodic signals (e.g., gene expressions for cell-cycles). We use a quadratic-optimization problem formulation in order to find the shape of the signal and the properties of periodicity to find the exact period. Finally, we show the results of applying this method on the gene expression data for human fibroblast cell cycles.