The perihelion of long-period comets places them near the Sun so they may exhibit activity. Before 2013 LU28 reached its perihelion, we performed a continuous observation to detect possible activity. Using the Lijiang 2.4 m telescope with a Johnson R filter, we measured the brightness of 2013 LU28 from 2024 January 3 to April 13. The instrumental magnitudes were subsequently transformed into the Pan-STARRS r system. Due to the noticeable descending trend in the absolute magnitude, we verified the cometary activity and constrained some photometric properties of 2013 LU28. Consequently, the increased cross-sectional area had a rate of 42.8 km2 day−1, and the corresponding mass-loss rate was 2.64 kg s−1 with the assumption of a dust-particle size  and the density ρ = 400 kg m−3. We estimated the nucleus radius as 0.11 ≲ rn ≲ 0.21 km for CO sublimation and 0.20 ≲ rn ≲ 0.71 km for CO2 sublimation and the grain size of 2013 LU28 was ac ≃ 117.95 μm for CO and ac ≃ 7.57 μm for CO2. The long-term observations provided in this paper will offer significant value for investigating the mechanisms driving the activity of 2013 LU28.

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