The orange pulvinaria scale, Pulvinaria aurantii Cockerell (Hemiptera: Coccidae), is one of the most significant citrus orchard pests in northern Iran. To assess the population fluctuations of this pest and its predator Cryptolaemus montrouzieri Mulsant in Tonekabon blood orange orchards, 80 leaves from 20 trees were randomly selected at each sampling time (with a maximum relative variation of 15%) and the number of each biological stage of the P. aurantii and its predatory ladybird were recorded per leaf. The average population of all biological stages of P. aurantii (ovisac, nymphal stages, and adult female insect) peaked on June 29 (30. 05 per leaf) and September 14 (29. 55 per leaf) in 2011, and on June 21 (30. 09 per leaf) and September 6 (22. 6 per leaf) in 2012. Similarly, the average population of all C. montrouzieri biological stages peaked on June 29 (0. 34 per leaf), September 7 and 14 (0. 45 per leaf), and June 21 (0. 65 per leaf) and September 6 (1. 00 per leaf) in 2011 and 2012, respectively. The population change curves indicated that increasing the population of ovisacs, 1st and 2nd instar nymphs of the pest attracted and increased the population of C. montrouzieri on infected trees, possibly due to the desirability of these biological stages of the pest to the predator. The present study revealed that in both years, the second generation of the pest is characterized by greater concordance and overlap between the populations of scale ovisacs and ladybird eggs. In 2011, C. montrouzieri prevented an increase in the population of P. aurantii second generation, and in 2012, due to a higher population density, it was able to significantly reduce the second generation population of this soft scale. Additionally, the regression between prey and predator populations was statistically significant, indicating a density-dependent response of the predator to the prey population.