Background and Objective Telomerase activation is an important characteristic of the most cancers that prevents telomere shortening and finally cell death in cancer cells. Various studies have been investigated telomerase activity and telomere length in cancer cells. Despite recent progress in understanding the role of telomerase activity in cell viability, numerous questions such as telomerase activity in relation to telomere length remain poorly understood. The present evaluates mathematical relationship between telomere length and telomerase activity in some cancers. In addition, the study compares three types of human cancers in terms of both the telomere length pattern and telomerase activity. Materials and Methods Based on the presented raw data in various literatures, we assessed the mathematical relationship between telomerase activity and telomere length in some human cancers, including melanoma, ovarian and leukemia. Mathematical analysis has been performed using MATLAB. Findings Telomerase activity exhibited almost periodic fluctuations over telomere length in cancer cells. A third order Fourier model has been fitted to data for three cancers. The R-square and some of square error (SSE) methods found to be 1 and very near to zero, respectively for all the cancers in this study. Normalized cross-correlation has been used to compare the pattern of fluctuations in the cancers with each other. Interestingly, the periodic fluctuations look similar in the above mentioned cancer cells. Conclusion In conclusion, telomerase activity and telomere length have similar oscillatory behavior in melanoma, ovarian and leukemia cancers. Further analysis is required to uncover the relevance telomerase activity with telomere length in primary tumors and metastatic cancers.