The decrease with time of TL intensity in LiF:Mg,Cu,P TLDs: Chinese GR-200A (produced by the Solid Dosimetric Detector & Method Lab., Research Institute of Chemical Defence, Beijing, China) and Polish MCP-N (made by TLD Niewiadomski & Co., Kraków, Poland) was studied at room temperature over periods ranging from 10 minutes to 3 months. All detectors which underwent a standard annealing procedure were read out in a Harshaw 5500 hot nitrogen reader using a 8°C/s linear cycle over the range 60–300°C. Each peak was analysed using the GCA glow curve deconvolution program, specially designed for this phosphor. We confirm the expected slow exponential decrease for each peak, finding that the fading of peak 3 in GR-200A LiF:Mg,Cu,P appears to more rapid than that in MCP-N. We also present the time dependence of the ratio of peaks 2 and 3 with respect to the main peak. The knowledge of such ratios could be useful in assessing the time between exposure and readout for periods of up to about 3 months.